Note to Self:

Fixing robots can be hard if you forget the robots exist halfway through the operation.

Memo to myself: Do the dumb things I gotta do

Touch the puppet head

—They Might Be Giants, "Put Your Hand Inside the Puppet Head"

Dear self,

I know you may find this hard to believe, but it was actually you who wrote this page. Upon learning of a Government Conspiracy (though it could have very easily been an Ancient Conspiracy), you decided to investigate. Unfortunately for us (remember, I am you from the past), the local Big Bad found out and decided to make you forget everything through Laser-Guided Amnesia, even implanting Fake Memories to throw you off. As he warmed up his Applied Phlebotinum, you quickly scribbled this page on the first piece of available medium you found. It could have been ourself, a piece of paper, the floor, a videotape, or the back of a DNA-tracking device. If you're wondering why you chose a wiki where anyone can get at this note and alter it, well... it was there.

As proof that this isn't some sort of elaborate hoax, I'll mention that weird dream you had when you were ten involving the Care Bears, even though that only works if you still have at least some memories left. There, now you know that I am you.

Without this piece of evidence, you can't continue your battle against the big unknowing evil. Waking up with this message could be the beginning of a series (if you lived in a TV show, which you don't) or a defining trait of your character. Knowing of the existence of this conspiracy could very well turn you into Agent Mulder, as you will immediately believe it was you that wrote this, even if some people say those who suffer from amnesia have trouble accepting they DID write something. It's like a Memory Gambit, except it's a last ditch effort rather than premeditated as part of a convoluted plan.

While you may not even know your own name, this is, for all we care, a Call to Adventure!

Respectfully, Self.

Don't forget:

Anime and Manga

A variation happens in Code Geass. After finding out Zero's identity, Shirley Fenette is shown writing in her journal about everything that's happened lately, but ends up tearing it out and throwing it away. Later, after she's been mindwiped, she finds the page under her desk.
Subverted in Tenshi na Konamaiki, where one character comes to a confrontation with the genie ready to secretly take notes. He discovers a vital secret about the genie during the meeting, but their group gets Laser-Guided Amnesia at the very end. Shortly afterward, he discovers and pulls out the Note to Self:... which contains not the secret bur rather some other perverted fact he had witnessed at that time, which given his character got the higher priority.
In JoJo's Bizarre Adventure Part 3, the heroes are attacked by a Stand-using baby who can attack and kill them in their dreams, and even if they survive, they won't remember the attacks after they wake up, because people quickly forget their dreams. Kakyoin warns himself about this by carving the message "BABY STAND" into his arm.
- Part 6 had Jolyne sewing notes on her own skin using her own stand when she was under the effects of Jailhouse Rock which makes her unable to take in more than four pieces of information.
In Re:LIVE the main character is framed for murder and begins to write himself a note to jog his memory in anticipation of being subject to Laser-Guided Amnesia along with the implantation of a new personality as per the law. In looking for a place to hide the note, he realizes he already did this the first time he took the fall for the real murderer - he had nowhere else to hide the note but inside his own body, so he cut open the skin over his stomach and hid the note with a photo of the real murderer inside his own body.

Fan Works

Bella of the Alternate Universe Fic Luminosity does this all the time. She would like to do it more, but since not everything she wants to write down can be public knowledge, can't. This is one of her reasons for wanting to be a vampire: perfect memory.
The Magic of Torchwood a Harry Potter/Torchwood crossover does this twice, first Future Jack sending the team a video message and Gwen when she gets rid of Adam. Again.

Film

The main character from the movie Total Recall used two video messages. These set up some of the best lines and scenes in the movie.
- Turns out that he came up with the plan and is manipulating himself with the clues he left behind to function as the perfect mole. It's not every day you Mind Screw yourself on purpose.
Done by the protagonist in the movie Memento, using pictures as well as tattooing information onto his skin.
- He also only trusts notes to himself that are in his own handwriting. At one point another character insists that he write something down that he doesn't believe is true, so he purposely writes it in different handwriting so that he won't believe it when he reads it later.
Chris Pratt in The Lookout, who has a bad short-term memory due to a serious head injury and needs to write everything down just to get through the day.
In the film The Machinist, the main character unknowingly leaves post-it notes of a game of hangman to unearth the suppressed memory of his fatal hit-and-run.
In the film 50 First Dates, the main character Lucy keeps a journal (later a video tape) since she loses her memory every day.
One of the protagonist's envelopes in Push is addressed to himself.
- Kira also leaves a short message for herself written in her lipstick on a mirror. She even checks to make sure it's her own handwriting.
A running gag with comedian Norm MacDonald, used extensively in the movie Dirty Work. Could be seen as the Trope Namer.
In Bill and Teds Excellent Adventure, the title characters find a note left by their future selves at the police station. More often, this trope is evoked throughout the movie in a fashion similar to the Norm MacDonald example above.
Similar to Memento and 50 First Dates, the Dana Carvey film Clean Slate is about a private investigator suffering from anterograde amnesia, using a tape recorder to leave himself notes.

Literature

The protagonist of the novel The Raw Shark Texts finds one of these after waking up on his bathroom floor with absolutely no memory due to the memory-eating shark that has been hunting him.
Artemis Fowl puts together a slightly more complicated version of this (involving a video-message, among other things) as part of a Memory Gambit in his own book series after being mind-wiped in the third book. It comes to fruition in the fourth.
The protagonist of the 1952 short story (quite possibly making it the origin of this idea) and 2003 film Paycheck did this with a bag full of random items triggering a Gambit Roulette to act as the proof.
Tally Youngblood had to write her future self a note in Uglies, because after she underwent the traditional surgical procedure that made her a Pretty, she would forget all the plans she had made beforehand to eventually reverse the process.
Gene Wolfe's Soldier of the Mist and sequels are written as the journal of the hero, Latro, who has anterograde amnesia, constantly losing his memory of the previous day. The first words of the journal are "Read this each day."
Discworld: the Time Monks force Sam Vimes to do this to himself so they can tell him sensitive information without letting him remember it. Sam being who he is, he figures it out again anyway.
Real life example: in one of his early essays, David Sedaris talks about his first boy-crush attempting to out him at summer camp by showing off a note that he claimed to have found on David's bed. The note read, 'I like guys.' Present-day David speculates that presumably, the idea was that he'd written the note to himself, in case he somehow forgot that he was gay.
There's one SF short story where aliens steal all human memories - each night, those of one more day, going back in time. People have to employ this for a long time - more than a decade, in fact.

Live Action TV

Daniel Faraday apparently did this at some point on Lost. He's surprised to find the note "If anything goes wrong, Desmond Hume will be my constant" in his journal.
- It's later revealed that Daniel suffered from memory loss due to a botched time travel experiment, and his past self who wrote the journal knew about Desmond and the other information there due solely to the Stable Time Loop created in that episode.
Gwen Cooper in the first episode of Torchwood, but she wasn't as successful.
In Doctor Who series 6, when team TARDIS faces an alien that you can't remember the moment you look away, they leave notes to themselves (often all over their body) telling them what to do. Paranoia Fuel at its finest.
Bennett from Heroes leaves himself a note saying "Claire's safe. She's with friends." after he sends Claire away to keep her safe from the Company and has the Haitian wipe his mind of any memories that could possibly lead them to her. His wife gives him the note, telling him he wrote it.
Doesn't involve amnesia, but in How I Met Your Mother a Running Gag is that the characters occasionally write letters to themselves addressed 'Dear Future Ted' and signed 'Past Ted'. It also gives us this little gem :

Ted: That is a tough problem. You know who'd know how to solve that one?
Marshall: Who?
Ted: Future Ted and Future Marshall.
Marshall: Yeah, let's just let those guys sort it out.

- Two months later :

Marshall: Damn it, Past Marshall!

Rodney McKay in Stargate Atlantis used a video message when everyone in Atlantis lost their memories in "Tabula Rasa."
In Stargate SG-1, Vala has her memory altered (so that she believes she was abandoned by SG-1) in a batmanGambit to capture Adria. She leaves a Note to Self: for after she is brought back, knowing she would be...rather upset with her teammates otherwise.
- Another episode, 2010, taking place in the then-future year of 2010, showing that the Goa'uld have been defeated by a benevolent and powerful alien race that SG-1 discovered. It is later revealed that the aliens have used their technology to secretly sterilize humanity so they can take over when everyone has died of old age. Jack is able to use the Stargate to send a message back in time warning his past self not to go to the star where they discovered the aliens. General Hammond immediately issues an order that the note's instructions be followed.
Star Trek: Voyager ("Unforgettable"). Chakotay falls in love with a beautiful alien from a species that fades from memory after a while. To ensure this they also implant a virus that destroys all computer records. To make sure he doesn't forget, Chakotay writes out what happened on paper.
Kurt Mendel in the Odyssey 5 episode "Time Out of Mind"
Upon waking up in Shibuya with Laser-Guided Amnesia, Tsuyoshi finds a note in his mouth written in blood that simply says, "LEAVE SHIBUYA. - RAVE". After the Restore, he pulls the same trick by swallowing one of Ema's fake fingernails, which is significantly more successful in jogging his memories.

Music

In the parody song 'bimbo nr 5' 'Bill Clinton' literally says 'note to myself, nail her later.'

Radio

Zaphod Beeblebrox in The Hitchhiker's Guide To The Galaxy, who was complicit in the memory wipe but left a message by burning his initials into his own brains.

Tabletop Games

One of the more entertaining abilities on offer in time-travel RPG Continuum is the ability to send yourself advice from the future.
- Also possible in the out-of-print Timemaster RPG if you're using the "Timetricks" supplement. (Core rules, it's a violation of the Laws of Time.)

Video Games

The protagonist of the old Cyberpunk platformer, Flashback.
The Practical Incarnation in Planescape: Torment, upon learning that he would lose his memory upon death, set up several contingency plans (including keeping a journal and tattooing his own back with instructions) to make sure that future incarnations would be able to follow in his footsteps and finish his work. Unfortunately for both of you, by the time the current incarnation of the Nameless One comes around, some of the incarnations who've lived in-between (amongst them the Paranoid Incarnation) have ruined most of them.
- Due to The Nameless One's Healing Factor the Note to Self: on your back was tattooed with a knife.

[Regarding the length of the tattoo]No wonder my back hurts; there's a damn novel written on it.

- Interestingly, the Paranoid Incarnation left a journal himself. Granted, it's an incredibly difficult puzzle cube with an instant kill penalty for guessing wrong... and he killed everybody who understood the weird language it was written in... but still.
- They also left behind various body parts, including his eye and arm, and hid stuff for you in your intestines.
Amnesia the Dark Descent starts with the player character waking up close to one of these, informing him that he wiped his own memory willingly, and now has to kill a certain baron of the castle he finds himself in.

Webcomics

In Freefall, Florence (an intelligent AI) has a safeguard which prevented her short term memory from being converted into long term. When it was activated, she used a Post-It pad and pen to remind her where she was going, what she was doing, and even the fact that her memory was affected.
- Including a note saying "skip to the end" because her memory was only about three minutes long, and reading all the notes she'd accumulated at that point would have taken too long.
At one point in Schlock Mercenary, when the entire crew was undergoing forced memory rewrites, Schlock used the properties of his Bizarre Alien Biology to store his real memories of the encounter inside a bit of himself, which he protected from the rewrite by shoving it inside one of his extra eyeballs. Schlock was smart enough to realize that he couldn't actually get the crew to remember what really happened—such an effort would most likely lead to them getting killed. Instead, he just made sure to tell himself to kill the bastard who did it to them.
Note to self: Don't kill Steve. "What have I done!?"
Wapsi Square. Stuck in a time loop, Brandi writes a book to her future self detailing how to get out of the time loop.
Adam and Jamie in Irregular Webcomic wrote to themselves to remind that Elvis Presley is alive before erasing excessive memories (including the info about Elvis) from when they drink from Mnemosyne river. Naturally, they don't believe it.
In Spacetrawler, Pierrot, upon learning that he's to be brain-wiped by the subterranean Mihrrgoots, writes himself a letter containing some very important information about the Eeb liberation mission he's on. After the mind-wipe, he finds the letter in his pocket... and he dismisses it, assuming that he just had too much to drink. Later, the letter ends up becoming important anyway--the king of the Mihrrgoots gains Pierrot's trust by referring to the contents of the letter.

Web Original

Most characters in Ruby Quest, if not all, are suffering from amnesia, and at least two people have attempted to counter this by leaving notes to themselves: Tom discovers writing inside his locker, advising him not to trust #7, i.e. Ruby - the reason is revealed soon, and results in a temporary break-up between the two. Meanwhile, the head doctor, Filbert, wrote a note that simply told that he has amnesia, which is why he can't remember things - as well as ensuring him that he is still clean.
Pretty much the entire point of Marble Hornets, along with other works in the Slender Man Mythos which take a similar vein.

Western Animation

Professor Denzel Crocker in The Fairly OddParents.
A kid who saw the first contact between humans and aliens in the Men in Black cartoon series.
On The Angry Beavers, Norbert recorded a tape telling himself how to regain his memories under the Genre Savvy presumption that he'd eventually be hit on the head by his accident-prone brother and get amnesia. It even contained a Shout-Out to Total Recall. His solution? Just let his brother hit him on the head again.
At the end of the Invader Zim episode "Bad, Bad Rubber Piggy", Zim desperately throws a note into his time machine and back into the past after severely screwing up the timeline. This somewhat works as the note switches places with his brain, leaving him a drooling moron holding a brain (and thus repairing the timeline). What it said? "ZIM, DON'T USE THE TIME MACHINE! LOVE, ZIM!"
Cruella de Vil on the One Hundred and One Dalmatians cartoon would make these, despite never actually having lost her memory (well, except that one time).
Stewie Griffin on Family Guy
The Histeria!! version of Christopher Columbus wrote one: "Never again hire anyone from Cabin Crews R Us."
Generator Rex: Rex suffers from chronic amnesia (as in he'll suddenly blackout and forget everything about his life up to that point.) During one of his "lives", he compensates by making a comprehensive journal for this purpose. However, Rex destroyed the journal upon realizing what an ass that past self was, though he's since started a new one.
Hank makes a video note in Venture Brothers when he has to have his memory erased after he sleeps with a woman, finally losing his virginity, only to discover that the woman was the mother of his best friend Dermott... and that his own father, Dr. Venture, was Dermott's actual father. Hank's note to self is something where he reassures himself that he got laid.
Dale Gribble does this in King of the Hill.

P.S.: The conspiracy is as follows - the government is run by reptilian aliens, Sasuke is Naruto's time-traveling father, you're a Time Lord and Everyone Is Jesus in Purgatory. Also, the Big Bad found us on the way to the supermarket. Get milk, soda, chocolate syrup, and a block of sharp cheddar.