Can't You Read the Sign?



"Sign, sign, everywhere a sign

Blockin' out the scenery, breakin' my mind

Do this, don't do that

Can't you read the sign?"

- "Signs", Five Man Electrical Band

"Now WHY would you go and do something like THAT?! Didn't you see the SIGN that said DO NOT PUSH THAT BUTTON?!"

- Mimiron, World of Warcraft

A humorous trope in which a posted sign or spoken warning against an action is so precise that you just know that the characters will do exactly that.

Not to be mistaken for Schmuck Bait, where the sign is the source of temptation. Instead, a Can't You Read the Sign forbids something that the characters were going to do anyway, or didn't realise was forbidden; often they take no notice of the sign.

Compare Not Cheating Unless You Get Caught and Rules of the Road. Also see Here's Your Sign, when the humor comes from the stupid things people say about the sign.

Examples:

Advertising

 * A commercial for Corn Pops has a sign at a zoo reading "Do Not Mesmerize Lizard With Delicious Corn Pops."

Anime and Manga

 * A favourite gag of Ranma One Half: in one instance, there was a sign saying "Do Not Break Wall". Ryoga, of course, broke it.
 * In the manga, Ryoga, thinking of Akane, hugged a pole that had the notice "Do Not Hug Pole". Because he's so strong, he broke the pole. And right above the former sign there was another, off-panel in the previous panel, which read "Do Not Break Pole".
 * Ranma's mom sat on a water main marked "Danger: Do Not Sit".
 * Pantyhose Taro was dangled from a tree with a sign on it reading: "Please do not hang people from this tree."
 * Soun and Genma were once knocked off a cliff by a sign blown at them by very strong winds. The sign -- of course -- read: "Danger! High Winds!"
 * Early in the anime, Ryoga falls down a hill next to a sign reading, "Warning: Landslide area"
 * Ranma was once running atop a the fence by the canal (as he does all the time,) when a section fell out, marked with a sign that read "Danger: Unstable. Do not stand on top." He quickly jumped onto the next section... which read "Also unstable" and dumped him into the water.
 * One of the more humorous examples had a one-shot character waiting for Kodachi at a garden while doing a Noblewoman's Laugh. Naturally, there was a sign right outside that said "Please do not laugh loudly inside the garden."
 * Needless to say, Rumiko Takahashi loves this gag, and it appears several more times.
 * Haruhi Suzumiya never met a sign she didn't promptly ignore, such as the NO DIVING sign during the pool scene in "Endless Eight", while Kyon has never missed a sign that he didn't suffer for. At least, not yet. R.I.P., Kyon's Bike.
 * At one point in Yotsubato, Yotsuba leans over the arm of an escalator... and hits her head on a sign warning not to do just that.
 * The ubiquitous, not-once-respected "No Smoking" signs from Cowboy Bebop.

Comic Books

 * Phil Foglio is fond of these as background jokes in his various comics. As an example, in a Mad Scientist's lab in XXXenophile, there was a sign on a complex piece of electrical equipment reading, "Do Not Place Tongue Here. Again".
 * No Leaning on the Sign
 * This Nodwick strip. The content says it all, really.
 * A one-panel scene in Scott Pilgrim's Precious Little Life shows him sitting on a couch, right next to a sign that says "Do Not Sit". The Movie reproduced the scene as well (Director Edgar Wright states in the commentary that he thought it was one of Brian Lee O'Malley's best jokes).
 * Played for laughs in a Donald Duck story. He and his nephews went to a foreign country and the nephews climbed a wall. On the other side of the wall, a furious man called their attention to a sign at the top of the wall and asked if they couldn't read it. As the sign was written in the country's language instead of one they knew, the nephew who answered truthfully said "no". (Note: The wall was so high nobody would be able to read the sign without climbing it first)

Film

 * Spaceballs: the auto destruct button has a sign warning not to press it. Also doubles as Schmuck Bait.
 * Not Another Teen Movie has a sign on the ventilation duct work stating "Limit Two Horny Teenage Boys". When three try to use it, it breaks.
 * When we first see Areola, she's standing naked in a school hallway next to a sign that says "Dress Code Strictly Enforced".
 * The guitar store in Waynes World had the sign "NO Stairway". This sign is based off the real world: so many people would come into music shops and test the guitars by playing "Stairway to Heaven" that clerks would hang those signs. On home video releases due to music licensing issues; in the original theatrical release, Wayne did play Zeppelin's classic, but on video, it's a Suspiciously Similar Song. If anything, that makes it even funnier. "No Stairway! Denied!"
 * Some shops also have a similar sign reading "Customers playing "Smoke On The Water" may seriously wish to reconsider their motives in buying musical instruments." "Sweet Child of Mine" and "Freebird" have also been given this treatment. Working in a music shop must be hell.
 * Played with in the Discworld novel Soul Music, although there's no sign in Blert Wheedon's guitar shop; the "warning" that you shouldn't play "Pathway to Paradise" is when a troll rips your arms off.
 * The French movie La Cite De La Peur starts with a very poor slasher film in which a hammer-and-sickle-wielding killer is thrown into a puddle of oil fuel. Next to said puddle is a sign saying "OIL FUEL. DO NOT JUMP IN THERE". When the killer is thrown in the puddle again, the sign now says "OIL FUEL. DO NOT RE-JUMP IN THERE".
 * Let's not forget "Choucroute interdite" ("Sauerkraut forbidden.")
 * A classic example is the scene in The Wizard of Oz when Dorothy and the others arrive at Emerald City. After ringing the bell, the doorman tells them "Can't you read the sign?" He then realizes he had forgotten to put up the sign which reads "Bell out of order. Please knock." It is also evidentially the Trope Namer.
 * In the park in which the Burly Brawl in The Matrix Reloaded takes place, a posted sign reads "No Brawling". Neo rips the sign out of the ground and clobbers a Smith with it.
 * Scary Movie begins with a woman running away from the killer. She reaches a sign which points in two directions, one "Safety", the other "Death". Guess which one she picks.
 * In Sgt Bilko, we get Bilko sitting behind his desk in the motor pool, in front of a huge no smoking sign. "We have rules!" {lights match on sign) "Rules and regulations!" (lights cigar with match, takes puff)
 * Bedknobs and Broomsticks features a hapless bear who catches the magical bed while fishing, and tries to throw Miss Price and company back into the sea because "Can't you read reading? No Peopling Allowed!"
 * Lindsay Lohan's character in Just My Luck tries to sit down at a restaurant and get a glass of water, but the Funny Foreigner manager tells her "No buy no sit!", then points out a sign that actually does use those exact words.
 * In Airplane!! 2 there is a sign on some fuel barrels saying "Flammable. No Smoking. No Spitting." One character lights a cigarette and throws the match at the barrels - Nothing happens. Another character spits at the barrels causing a huge explosion.
 * Max Keebles Big Move played on this a bit: When Megan meets Jenna for the first time, Jenna tells her that the seat she's sitting in actually belongs to her. Megan asks if it has her name on it or something, to which Jenna reveals that the seat does, quite literally, have her name on it.
 * Lady and The Tramp features a scene where Lady, after getting muzzled after a clash with mean Aunt Sarah's two Siamese cats, is taken by the Tramp to a zoo where he knows a beaver that will help him get the muzzle off. There is a sign that says "No Dogs Allowed" at the entrance of the zoo. The Tramp gets around this by inciting a fight between the guard and a visitor, allowing him and Lady to enter the zoo undetected.
 * The Producers: About 1500 people pay big bucks to see a Broadway musical called "Springtime For Hitler". There's little doubt that the title was on the marquis, the posters and the Playbill. And yet they're shocked to see an opening number with dancing Nazis?

Literature

 * Used as a weapon in the Discworld book Thief of Time against powerful beings called the Auditors. Since the Auditors follow 'laws' and are actually the ones who file the paperwork for them, they obviously must respect what the sign says. Of course, when the signs in question are nonsensical, like an arrow pointing left that says "KEEP RIGHT"...
 * And when presented with a sign prohibiting the feeding of the elephant - the Auditors are compelled to seek out an elephant to not feed.


 * It's also occasionally referenced that an AM citizen/Wizard, upon encountering a sign not to perform an action will immediately perform the action just to see what all the fuss is about.
 * Also crops up in the Nomes/Bromeliad Trilogy, although in this case the nomes don't understanding the signs (or indeed a lot of other parts of our world).
 * Tom Holt's book Who's Afraid of Beowulf? had some Vikings encountering the many signs on the London Underground escalators, and are almost stumped by the one saying "Dogs must be carried". Thankfully, they have a Shape Shifter.
 * Polish book Krzyżacki Poker (in English it would be Teutonic Poker, as in Teutonic Knights Order) utilises this on the cover - we see character smoking right under sign "Rauchen Verboten" ("No Smoking" in German).
 * In the Kingkiller Chronicle series, taverns near the Arcanum have signs reading "No Sympathy" where "Sympathy" is a form of Functional Magic. Kvothe points out that these signs are likely confusing to persons unfamiliar with magic.
 * A hilarious inversion in Just Annoying by Andy Griffiths. Andy takes one of his neighbour's garden gnomes on holiday and sets it up for a photograph (for a postcard) on the diving board at the swimming pool. The lifeguard catches him and tells him that garden gnomes are banned from the pool. When Andy correctly points out that this is not on the sign (which he even checked beforehand), the response is "It shouldn't have to be, it should be obvious."
 * Just Stupid has a running gag where a park-keeper points out signs ("Keep off the Garden", "No Swimming") shortly after Andy has broken the rule in question, which eventually drives him to try and chase Andy out of the park. Andy's attempts at Loophole Abuse do not help: "I look around to check there's no signs saying "No Scooping". No, only one that says "No Fishing." Or more brazenly, "As far as I can see there is no sign around here saying 'Do Not Dismantle the "No Fishing" Sign and Turn It Into a Scoop'"
 * In one of John Bellairs's books, Miss Eells blatantly ignores a "No Trespassing" sign as she and Anthony hope a fence to explore an empty house. The narrator notes that Miss Eells hates such signs anyway, and once stomped on one just to show what she thought of it.

Live Action TV

 * In one skit on All That, the actors admonished a studio audience member for bringing a sheep into the studio. He protested, saying "I didn't see a sign!" At that point they indicate a large "NO SHEEP" sign on the wall.
 * A sketch by The Two Ronnies includes a sign saying "Do Not Throw Stones at This Notice".
 * Earl of My Name Is Earl is asked to make a shiv while in prison. He examines an array of improvised knives on glass display, with a sign saying "Don't make any of these".
 * Punningly parodied in the 1960s British sketch show We Have Ways Of Making You Laugh. Two villains are about to throw their captive into an incinerator, until he notices a sign which reads "Refuse to be placed in incinerator", and does so.
 * The Sesame Street special "Don't Eat The Pictures" features one of these in the Metropolitan Museum of Art. Guess what it says. Of course, Extreme Omnivore Cookie Monster find this difficult.
 * This was in fact a real sign that was in the museum at the time.
 * In an episode of Buffy the Vampire Slayer, Spike lights up a cigarette while framed by a "No Smoking" sign. In a hospital, no less. Harmony, however, looks embarrassed and snuffs hers out when the sign is pointed out to her.
 * In Hush, after everyone's lost his voice, Riley and Forest take the elevator down to the Initiative, but can't provide the voice ID and the elevator starts to fill with deadly gas. They're rescued before they asphyxiate, and after letting them out, Professor Walsh points out the sign that reads "In case of emergency, use stairs".
 * Also used for ominous Foreshadowing -- at the end of "The Harvest" Angel appears to be standing next to a sign saying WATCH YOU -- appropriate enough for his Mysterious Watcher role. But when he walks away we see the sign actually reads WATCH YOUR STEP, foretelling his Face Heel Turn into Angelus. Similarly at the end of "After Life" Buffy's other vampire Love Interest, Spike, is standing next to a discarded door with a BEWARE OF DOG sign, hinting at the Destructive Romance to follow.
 * In the first episode of Flight of the Conchords, Sally breaks up with Jermaine in front of a sign that says "No Dumping".
 * One of the common bits on Trigger Happy TV was Dom Joly standing in front of an enormous picture of himself labeled 'DO NOT TRUST THIS MAN' and talking to people, giving them directions and such.
 * In an episode of Corner Gas, Lacey tells Karen not to play with her hackey sack in the restaurant. Karen says that if it's a rule, there should be a sign posted, to which Lacey replies "We don't have a sign for everything. Read the sign!" and then points to a sign that reads "We don't have a sign for everything. -Lacey".
 * In an episode of Home Improvement, Tim Taylor and Jill Taylor decided to each test drive a tank, and Tim manages to plow several things over, including a sign that said "Tank Crossing" that was conveniently right in his path.
 * When the Tool Time crew visited an aircraft carrier, a large sign on the deck was modified to read, "Beware of jet blast, propellers and Tim."
 * In the Monk episode "Mr. Monk and Little Monk", Monk and Natalie had to stake out at a biker bar to identify the patrons who killed Gladys, the housekeeper of an old friend of Monk's. Monk attempts to tell a biker at the bar that he shouldn't be smoking and points to a no smoking sign right above the biker. Not only did the biker not stop smoking, but the biker simply reached up for the sign and set it on fire.

Music Videos

 * In the quasi-patriotic video-clip for the Dutch song Vijftien Miljoen Mensen the iconic image is a picture of a "Do Not Walk On The Grass" sign behind which are dozens upon dozens of people walking, talking, picnicking and doing other assorted things on the grass.
 * In a Michael Jackson film a cop turns up to tell Jackson off from Moonwalking, pointing to the no moonwalking sign.

Newspaper Comics
""Do Not Give the Birds Dutch Rubs"
 * The Far Side did this a few times:

"Keep Off the Dog"

"No Projectile Vomiting""


 * One B.C. strip has a character see a sign that says "Do not stand in front of sign". He tries to walk past it, but the other side says "Do not stand behind sign". The last panel shows him standing on top of the sign, a helpless expression on his face.
 * The same character, standing and staring at a sign, implicitly for quite a while. When someone comes along, he asks them, "Hey, what does 'loitering' mean?"
 * Other signs have included "DO NOT EAT THIS SIGN" (Grog ate the pole and spat out the sign) and "DO NOT STAND ON THIS SIGN" (cue rebellious caveman standing on it, despite gravity being 90 degrees from the position he was in)
 * In Bloom County, signs reading reading "No toad sexing" or other strange restrictions could occasionally be spotted in the background.
 * A visitor to MIT will find the words "No toad sexing" scrawled on the walls in numerous out-of-the-way places. The exact origin of this is disputed.
 * The US Acres strip used it quite a bit (in the first link, starts near the bottom).

Video Games
"Nefertiti: Hold it right there, Buckos! Can't you read hieroglyphics?!
 * In the third Kyrandia game, one section involves navigating sheer-faced cliffs and waterfalls, and the only way to go is up or down with the aid of certain items. There are signs posted on each screen that inform what items are not allowed ("No climbing shoes", "No umbrellas", etc.) However, it's reverse psychology. The forbidden items are the items that will work.
 * Similarly, the treasure chest and fishing minigames in The Legend of Zelda Ocarina of Time are hinted to have banned items; these items can of course be acquired and used to your advantage. (However, in the case of the sinking fishing lure, you do get a notice on your catch saying it was caught with an illegal lure.) But in that case, you can make it legal.
 * A Link to The Past has a signpost warning people not to throw objects into an obvious circle of stones sitting nearby. Not only is doing so the only way to get an item required to beat the game, but in this game, signposts themselves can be lifted, making it far too tempting to obtain the item by throwing the signpost.
 * There's another sign in A Link to the Past that warns you to pay no attention to the man standing next to it. If you go up and talk to the man, he's silent. But if you steal his sign, he gets a bit annoyed and starts following you around...
 * In pretty much any Zelda game ignoring odd signs is considered wise.
 * Pokémon Red and Blue. "Don't touch the poster in the Game Corner. There's no secret switch behind it!"
 * In Mad World, you can impale a Mook in the head with a sign. Guess what the sign warns you about?
 * In the first Oddworld game, inside Rapture Farms, there are various signs of this kind. For instance, near the beginning, "NO TALKING! To fellow employees", referring to the game mechanics of Gamespeak.
 * Indeed, if the player DOES try to talk to one of his fellow employees who is next to a Slig, and the employee responds, the Slig will shoot and kill him. Obviously, Rupture Farms takes their no-talking policy very seriously.
 * In Earthbound you are warned of in one cave about "Falling Objects". Then the photographer drops from the ceiling to take a picture of you. Granted, he always drops from the ceiling.
 * In a similar light, after visiting the Giant Step, Captain Strong stops you on the way out because of the DO NOT ENTER sign outside the shack (the letters are big enough for the player to read). You have to then go to the Police Office to wrap that issue up and proceed to Twoson. Yes, this is part of the plot.
 * In Donkey Kong Country 2, signs are used to indicate where animal friend sections end. Trying to cross the sign while riding one (or assuming the form of one) will cause the poor creature to inexplicably disappear and provide an extra life balloon.
 * The online promotional materials for Prinny Can I Really Be the Hero include this video. Sorry, no Prinny allowed!
 * Parodied in Lunar: Silver Star Story Complete. In Meribia, there's a sign on one house that's blocked by a bunch of flowers, making it impossible for anyone in your team to read. After Kyle joins the team, you can bring him to examine the blocked sign. Kyle resolves to find out what the sign says by walking through the flowers and pretty much destroying them. So what does the sign say? "Please don't step on the flowers."
 * Any time Snake smokes in Metal Gear Solid 4: Guns of The Patriots there is a "no smoking" sign behind him.
 * Not the only time Snake could invoke this trope: In Metal Gear Solid: The Twin Snakes, some of the armory's rooms have the words "No Smoking" in big letters, and if you equip the cigarettes... well, it speaks for itself. May have also been in Metal Gear Solid.
 * Similarly, Bill in Left 4 Dead does this in the No Mercy campaign. He sees a No Smoking sign and retorts with "That's a crock of shit!"
 * Full Throttle plays with it. "Do not play in or around Dumpster, do not sleep in Dumpster, do not Kick Dumpster, Usage of this container for disposal of human remains in this container may violate health ordinances". Ben observes this after taking a nap in the dumpster, being disposed of in the dumpster, playing around in the dumpster, and kicking the dumpster.
 * Revolution X has this, in which Helga writes a bunch of "do nots" on a chalkboard, these of course include stuff like, "Do not open secret areas", "Do not collect powerups", etc.
 * Sam and Max Freelance Police:
 * In Sam and Max Save the World, there's a sign above the freezer in Bosco's store that reads 'Tongues Placed on Freezer Become Property of Bosco'.
 * In Sam and Max: The Tomb of Sammun-Mak, the great grand-dads of Sam and Max are about to intrude on the maiden chamber of tomb guardian's daughter Nefertiti. The sign, naturally, is in hieroglyphics:

Maximus: It's a tern, and a leaf.

Nefertiti: Exactly. Turn, and leave!"

"Maya: Clean it or die!"
 * In The Sims 3, one of the towns features a river that happens to pass by the local cemetery, where there is a "No Fishing" sign posted on the river bank. If a highly skilled angler goes to that specific place between the hours of midnight and 4:00 am, s/he can, with the correct bait, catch the elusive Deathfish. Not only does the Deathfish have a high simoleon value if sold, it's one of the two ingredients used by a highly skilled chef to make Ambrosia, which makes its eater grow somewhat younger.
 * Ace Attorney: Justice for All: when Phoenix and Maya investigate a really dirty and greasy cafetaria, Maya notices that apperently no one cares about the "Keep our cafeteria clean" sign. Her suggestion is a bit more threatening:

"The A's: "OGRES ALLOWED SPARINGLY""
 * In Nancy Drew: Ghost Dogs of Moon Lake, there's a post-it note that reads, "Rotten Floorboards! Watch your step" except Nancy has to step right on the rotten boards to get a clear view of the sign.
 * A somewhat meta example from Mother 3: A sign obstructing the scenery warns you not to obstruct the scenery by posting signs.
 * After the Time Skip, a sign beyond a flowerbed begins to admonish you for stepping on the flowers in order to read it, before conceding that it's really the fault of whoever put the sign up in the first place.
 * This TAS of Family Feud features several such 'signs' in its middle section.


 * Magical Quest Starring Mickey Mouse (along with its GBA remake, Magical Quest Starring Mickey and Minnie) has a notable inversion of the trope. In the Fire level, the second level to be specific, Mickey (or Minnie, if the player decided to play as her in the GBA remake) arrives at a glass pane containing a fireman's suit that has a sign above it stating that, if there is a fire, someone has to break the glass. As if on cue with his/her entry, a block falls down and smashes the glass and has the fireman's outfit land near Mickey/Minnie, earning him/her the outfit.
 * In one town in Dragon Quest IX, there is a small plot of land being used for crops, in the middle of which is a sign saying "do not step on the crops". Naturally, due to its placement and the way you read signs in Dragon Quest games, the only way to read it is to step on the crops.

Webcomics

 * When the cast of the webcomic Yosh! visits Japan, the lead female is assaulted by flash perverts in a park, using a classic Japanese tag-team trick, where one sneaks up behind a woman and lifts her shirt, while the other is hidden in front with a camera. After she's 'dealt' with the two, Yosh comments that there should be signs warning against such assaults. Cue a frame showing several signs hanging and standing all over the park, reading "Warning: Beware of Perverts". In Japanese, of course.
 * During the "Pirates of the Oceans Unmoving" arc of Sluggy Freelance, a flashback shows the time when Torg bought Bun-Bun from The Little Shop That Wasn't There Yesterday. Finding exactly what he's looking for, for just under what he could afford to pay, he's Genre Savvy enough to realize where he is, so he then asks the proprietor for a gorgeous, bikini-clad girlfriend for the single dime he had left. The proprietor then silently points to a sign that reads "Attempting to abuse Magical Shop's magicalness will incur a 10 cent penalty."
 * Girl Genius: If they'd looked closer, maybe that invading army would have noticed the sign on the gates to Mechanicsburg: "Trade Entrance. Invade in Front."
 * Also, there is a chewing-gum machine in Castle Heterodyne with a sign saying "Poison - Illiteracy Reduction"; people who can't read the sign will eat the chewing-gum and die.
 * Actually inverted in Alice! - In which the title character actually ignores the sign.
 * One Cyanide and Happiness animated short features two policemen brutally enforcing a sign labeled "Do Not Read", and another nearby sign, "No babies."

Western Animation
"Lisa: Excuse me, when does the bus get to the museum?
 * In the Futurama episode "The Farnsworth Parabox", Fry and Bender need to move through the Planet Express office undetected. Bender rips the hatch off a superheated steam pipe, above which is a sign that reads, "No Crawling Around". They climb in and, well...
 * Dexters Laboratory had a sign in a fence with a "stranger" drawn and a forbidden red line. A "stranger" looking exactly like it goes in, thus showing he was obviously breaking the law.
 * Similarly, the door to Dexter's room has several signs that say or otherwise mean "No Dee Dees". They're only there to let the audience know she doesn't read them.
 * The Simpsons has used this gag several times:
 * In "Homer The Vigilante", Herman shows Homer a "miniature version of the A-bomb" which "the government built in the fifties to drop on beatniks". Homer then goes into a day dream sequence where he rides the bomb a la Dr. Strangelove onto a group of beatniks only for it to cut back to reality where he's actually riding the displayed bomb. Herman then points out the adjacent sign reading "DO NOT RIDE THE BOMB".
 * There's also an instance early on in the episode with Homer's heart attack, when he begins a quiet prayer to God and is shushed immediately by the nurse, who points to a sign reading "NO PRAYING".
 * When Homer is injured in a prison rodeo, he is treated in the prison's medical facility. When Marge remarks that he's being very stoic about the situation, he says he can't complain, then points out a sign saying "No Complaining". The doctor says that the sign's only for the prisoners, so Homer starts letting it all out: "Oh, I hurt so much! And my job is so unfulfilling..."
 * Lisa is trying to ride the bus to see a museum exhibit:

Bus Driver: [points to sign reading "Do not talk to driver."]

Lisa: Sorry, it's just that this is the first time I ...

Bus Driver: [taps repeatedly on the sign]

Lisa: End of the line?! I thought this was Bus 22!

Bus Driver: Yep, Mondays and Wednesdays. On Tuesdays and Thursdays it's the 22-A.

Lisa: 22-A?!? But that doesn't ...

Bus Driver: Don't make me tap the sign."


 * In order to protect himself from Homer, Bart hid behind a sign reading "Report Child Abuse".
 * When they made a Parody of The Da Vinci Code, Lisa entered a place that had a sign forbidding it. Under it, there was another sign alternatively allowing it, stating it was a sign, not a cop.
 * When Homer got lost inside a labyrinth, he tried to climb his way out but for electrocuted. He then found a sign stating it was electrified. Out of anger, he punched it and got another shock. He then found a sign reading "Signs also electrified".
 * The Critic used it a few times:
 * In a car chase between Jay and a studio exec in LA, the freeway sign reads "High-Speed Chases use Diamond Lane".
 * Jay talks to a cab driver. The driver (suitably foreign) says "Look at sign!". It reads "Driver knows only three words of English."
 * After Jay imagines the Statue of Liberty undressing for him, a policeman points at a sign reading "No fantasizing about statue."
 * Parodied in the Timon and Pumbaa animated series. Timon narrowly escapes a piranha infested lake and complains that there should be a sign. Pumbaa replies "Like this one?" and points out a plain looking sign next to them saying "Beware: Piranhas". Timon tries to save face by saying the sign should be bigger and Pumbaa points out an even bigger sign with spotlights and the same word written in lights.
 * And that one time when the two are in a runaway jeep headed toward a cliff. (It Makes Sense in Context.) Of course, there's dozens of signs on the path leading to the cliff, and they just crash right through them. CLIFF AHEAD! *smash* STOP NOW! *smash* SERIOUSLY! *smash* THESE SIGNS *smash* ARE EXPENSIVE! *smash*
 * The Emperors New Groove has a "No Llamas" (a llama with a line through it) sign at the diner.
 * An even earlier example; the Merrie Melodies cartoon "A Day at the Zoo" had an old lady at a zoo trying to sneak some peanuts to a monkey. He throws them back at her and shouts "Hey, sister! Can't you read?!", holding up the "do not feed the animals" sign for emphasis.
 * The Ed Edd and Eddy episode "Stop, Look, and Ed" used these as part of the plot. Eddy doesn't want to follow the rules and convinces the other kids to ignore signs as well. Also, Ed goes under some grass instead of on it due to a "Keep off the Grass" sign, and Edd is forced to concede "Well, I suppose Ed's not technically on the grass..."
 * In the Tex Avery cartoon Who Killed Who, a detective ignores the "Do Not Open Till X-Mas" sign on a door and tries to force it open. Santa Claus himself shows up to admonish him: "Can't you read?"
 * In an episode of Spongebob SquarePants, Squidward is closing up shop at the Krusty Krab and puts up the CLOSED sign just as a customer walks up. He asks if they're open, to which Squidward replies, "Read the sign." The customer then immediately makes an order.
 * In the Peanuts special, Snoopy Come Home, Snoopy is continually frustrated by signs that prevent him from going where he wants and doing what he wants, either in general or because he is a dog. Snoopy was actually happy with the last one he saw because it was at the building his previous owner lived and he could it as an excuse not to return to her. (Not that he hated her, he just liked Charlie Brown better)
 * In Family Guy, when Peter and Lois are buying fake documents at a supermarket in Cuba, they realize they have no money and ask the cashier if they will accept bits of string instead. The cashier replies, "Sorry, store policy" and points to a sign noting... that they don't accept bits of string.
 * Chowder and Mung once hid behind a sign that forbade hiding behind it. Not that the sign would be a good hiding spot regardless of what it read.

Real Life

 * Sign sometimes seen in science labs: "Caution: Do Not Look Into Laser With Remaining Eye".
 * Another favourite "Caution: Only bring cheap watches /credit cards you weren't planning on using anymore near magnet."
 * At least one lab has a sign in the hallway reading: "CAUTION: Active Robot." Do not stand in its way, or else.
 * A collection of bizarre signs, some of which fit the trope, including this "no kissing" sign.
 * Oddly Specific is a blog devoted to these kinds of signs.
 * Back in the day in St. Louis, there was a wonderful greasy spoon that looked like it was a Hollywood set dresser's idea of a Midwestern diner. It was called "Irv's Home Cooking." When (inevitably) a drunk college kid would ask "Where's Irv?", the stock character waitress would snap her gum, point at the sign out front and say, "Cantcha read the sign? He's home cooking."
 * And finally, who HASN'T seen a "no standing" sign, only to stand next to it? ("Standing", in the first case, meaning the act of leaving your car running in the parking space)
 * 4 words...Slow Children at Play.
 * Overweight comedian Bruce Bruce has a bit involving him and his similarly heavy cousin going to all-you-can-eat restaurants and sitting down at the buffet itself to eat, using "Well, I don't see a sign!" as their defense when approached by the staff. He mentions that when they get up to go to the bathroom, the restaurant usually puts out a sign.
 * Thanks to Values Dissonance, this "No Durians" sign falls under this trope just because people might see it and want to try it out to see what's so bad. The main reason behind these signs are that Durians smell like crap. However; you're very unlikely to find the fruit itself outside of South-eastern Asia.
 * Related, but with a different intent are signs that read "No Peanuts" or "No Raw Onions". Given how sensitive Peanut Allergies can be...not really a laughing matter.
 * The "Raw Onions" case is incredibly specific, too - it's actually on a building at Colorado State University because a professor has a severe Onion allergy, just as bad as peanut allergies.
 * "No Turn On Red." The freedom to make a right turn on a red light was introduced in most of the US and Canada as a response to the gas crisis -- the idea being that if it's safe to turn, you might as well do it rather than waste gas idling at the light -- and it's now a standard part of drivers' education. These signs appear at busy or obstructed intersections and are among the easiest to miss because they tend to be small black-and-white signs. (Not to mention, shrubberies can block signs off.) It's a fair bet that if you've driven a car in a medium- or large-sized city in North America, you've blown one of these signs without noticing it.
 * An anecdote about the Civil War Battle of Gettysburg: On the first day of the battle, part of the Union army's XI corps had taken up a position in the town's cemetery as a reserve position. During the events of the first day's battle, the rest of the Union troops were driven back into the cemetery by the Confederates. On the second day of the battle, a junior officer to Gen. O.O. Howard (the XI corps commander) jokingly pointed out a sign in the cemetery saying "Shooting and Use of Firearms is Prohibited" The officer asked if they would get in trouble for violating the sign. Shortly after, a cannonball struck the sign and destroyed it. Gen. Howard reportedly quipped "It appears the ordinance has been rescinded, and the shooting may go on".
 * There was a sign in a mall escalator in the Philippines warning about hitting a sign on the way up the escalator. In other words, it's a sign warning people about hitting their head on it. The real reason it was put up was to get people who aren't paying attention to hit their head on it and duck than to accidentally get them stuck in the wedge where the two escalators meet.