Neon Sign Hideout

The villain is an unstoppable force of evil! His evil lair is impossible to find! Hidden in the darkest corners of the planet! How will our intrepid heroes ever find it?

Oh wait, the giant, brightly lit sign proclaiming "This Way To Villain's Hideout!" Nice work!

Almost universally a Comedy Trope. Variations include, but are not limited to "Villain's Hideout, Keep Out", and "Evil Fortress, 100 Miles". Very common in Western Animation.

Sometimes, the sign instead advertises the Legitimate Businessmen's Social Club which is in no way a villain's lair, at all.

Examples of Neon Sign Hideout include:

Anime and Manga

In Astro Boy, the three robots' underground hideout is marked by a garishly painted sign.
A good guy example: Lupin III had his name written on the roof of his hideout in neon for one episode so the bad guys trying to assassinate him could easily locate him.

Comic Books

In one issue of Jughead's Diner, Jughead and his Dinersville pals have to lure a giant gelatin monster to the secret lab of Sal Monella, but don't know where it is. Luckily, there are signs pointing the way. ("See the secret lab!") When Jughead lampshades the concept of signs leading to a secret lab, one of his pals suggests that the lab was so secret even Sal couldn't find it!

Film

A version of this takes place in Spy Hard, as the villian's headquarters has a clearly marked "Intruder Entrance" sign on one of their doors, and it isn't Schmuck Bait either, it's actually pointing out the best place for intruders to enter.
The live-action Dudley Do-Right movie had this with Snidely Whiplash and his secret hideout.
The Wizard of Oz (1939): While going through the Haunted Forest to the castle of the Wicked Witch of the West, our heroes encounter a sign that says "Witch's castle 1 mile." Mind you, the Witch is the ruler of the country, and has no need of secrecy.
Quest for Camelot: Kayley says there should be a sign declaring the border of Dragon Country, despite the fact that the air suddenly turns gaseous, the sky is orange, and the heroes walked over a dragon skeleton to get there.
Megamind had a variation of sorts. Roxanne was able to easily find Megamind's hideout because it was the only building in town with a fake observatory on the roof, but she couldn't have gotten in without the doormat that said "Secret Entrance".

Megamind: Minion!
Minion: (Meekly) I kept forgetting where it was.

Literature

The various signs on the way to Don'tgonearthe Castle ("Last Chance Not To Go Near The Castle!" "Don't Go Near The Coach Park!") in Carpe Jugulum. Justified in that the Old Count wants visitors, and understands Schmuck Bait.

Live-Action TV

The 1960s Batman series, naturally.

Video Games

Bowser's castle in Super Mario World was marked with a literal neon sign proclaiming "BOWSER", though it wasn't trying to be hidden in the first place.
Serious Sam II sees Sam wonder where he can find the imprisoned Simba shaman right outside a building with a huge neon side that reads "Lucky's imprisoned Simba shamans".
In Paper Mario: The Thousand-Year Door, the "Secret Entrance" to the Great Tree is cleverly hidden by a large piece of paper that's the exact color and texture of the tree. You blow that paper away...and you find that the "Secret Entrance" has been marked thusly with a large movie-theater–style sign, complete with flashing lights around the edges.
- Hilariously, an NPC traveling with you, when talking about the Secret Entrance and how it's hidden, mentions that it wouldn't be marked by a sign.
Dragon Quest IV doesn't have a neon sign, obviously, but it does have an island shaped like a spider with four smaller fortresses in the northeast, northwest, southeast, and southwest corner.

Web Comics

Bob and George, with Wily's castle.

Western Animation

Darkwing Duck had a base with a giant flag.
- A bit of a subversion: Nega-Duck knows that Darkwing won't notice the huge flag, so he also leaves a single breadcrumb behind at the site of a fight between them, knowing Darkwing would figure out exactly where it came from.
In the 1946 Looney Tunes short "The Great Piggy Bank Robbery", Daffy Duck (as "Duck Twacy, the famous detec-a-tive") takes a streetcar (labeled "To Gangsters' Hideout") past neon signs that read, "Gangsters' Hideout," to one that reads, "This is IT! Entrance."
- Another Looney Tunes example: The 1952 Bugs Bunny short "Water, Water Every Hare" started with a shot of a castle with a neon sign alternating "Evil Scientist" and "Boo".
  - In "Bugsy and Mugsy" Bugs Bunny is living in an abandoned house that two criminals use for a hideout. Bugs invokes this trope by putting up a literal Neon sign that says "Rocky's Hideaway." naturally it doesn't take long for the police to find them. Rocky never noticed the sign and thought that idiot sidekick had turned him in. Poor Mugsy gets a beatdown for nothing.
In the The Fairly OddParents TV movie, Fairly Odd Baby, Wanda and the other were looking for the evil baby lair, and she said that her maternal instincts were a sonar device to locate Poof. She credited her maternal instincts to finding the room where Poof was located, but there was clearly a sign that pointed to wear the door was.
Also done in the Super Mario World cartoon, where Bowser's Castle has the same sign as in the game, except it lights up letter by letter. And is apparently called the Coney Island Disco Palace. A menacing name it is not.

Real Life

Driving around British country roads, every now and then you'll see signs directing you to a "Secret Nuclear Bunker" or similar. Generally it's because they're decommissioned and living a new life as tourist attractions, but it's still entertaining.