Crapsack worlds, especially Dystopian ones, tend to attract resistance movements, and sometimes they have to resort to crude methods to get the word out. Graffiti is one of those methods: it's easy to do, usually you can avoid getting caught doing it, and it's anonymous. Frequently uses the Icon of Rebellion.
Frequently Truth in Television.
The Wolverines from Red Dawn usually leave graffiti behind at the scenes of their ambushes. They also spray-painted the names of their dead on the side of a cliff (resistance Rock) as a memorial.
Shows up briefly in Rise of the Planet of the Apes, where the picture Caesar drew on his wall in the animal shelter to represent his window at home is seen spray-painted on a road sign following the apes' revolt.
In They Live!, Nada finds graffiti reading 'They Live, We Sleep', referring to the Resistance's knowledge of Aliens that rule over humanity.
Total Recall The phrase "Kuato Lives" graffitied around Mars, as a sign that the mysterious leader of La Résistance is still alive despite Cohaagen's attempts to kill him.
In the film Turk 182 the eponymous graffiti artist writes "Zimmerman Flew, Tyler Knew" plus his name all over town, in order to stir up trouble because his brother, a firefighter, got injured while assisting with a fire rescue while he was intoxicated and the department won't cover his medical bills. (He had been off-duty, but rushed to help anyway when he heard about a fire nearby.) Zimmerman was a Public Works Commisioner who had fled the city for an unspecified crime, and it is believed by some that Mayor Tyler knew about his crimes. Zimmerman doesn't actually have anything to do with Turk's grievance; it was already a graffiti meme when he started.
In Trickster's Queen, the last novel of Daughter of the Lioness, there are sightings of the freedom movement's Icon of Rebellion various places in the city: wall graffiti, carved into shop windows, implied by the arrangement of merchandise in street stalls, etc. About halfway through, the protagonist notices that somebody has carved a pattern of the symbol into the belt of the Statue of Our Founder in the center of the city. Near the end of the book, just before the final clash between the freedom movement and the occupying rulers, it's mentioned that the pattern has grown to cover the entire statue.
In Discworld novel Reaper Man, zombie Reg Shoe paints pro-undead-rights graffiti on any handy wall in Ankh-Morpork. Subverted in that La Résistance, in this case, consists of one overenthusiastic zombie who's only a heroic resistance leader in his own mind.
In Little Brother, this is done particularly in the Mission, with the "Don't Trust Anyone Over 25" slogan.
In Magicians of Gor Tarl and Marcus scratch deltas in public places to make it look like there's a "Delta Brigade" going around causing trouble, in reference to a recent military loss in a delta. Then they start to find deltas scratched where they didn't do it...
The Moon Is a Harsh Mistress. The "Simon Jester" symbol (a matchstick drawing of a little horned devil with big grin and forked tail) was used in anti-Lunar Authority graffiti.
In the original miniseries, the graffiti "V" stood for Victory for the resistance.
In the remake it was inverted: instead used by pro-visitor youth groups as a form of propaganda, undermining the resistance. Instead "John May Lives" was scrawled as graffiti by the Fifth Column resistance.
The Dingees: The cover art of the album The Crucial Conspiracy features a propaganda poster in the Soviet style. Inside the liner notes, the poster is shown again defaced by anti-government slogans, and with a skull painted over the worker's face.
In an Evil vs. Evil example, in Bioshock 2 Lamb's followers write anti-Andrew Ryan (the Big Bad of the previous game) graffiti all over the place (including in UV ink on the posters which came with the collecter's edition of the game). Despite being his ideological opposite, Lamb isn't any better (indeed, in some ways she's worse given Ryan couldn't kill his own son even though he was a Laser Guided Tyke Bomb sent to kill him, while Lamb was willing to use her daughter as a test subject).
The main character of De Blob paints on buildings to restore color to the city he lives in, which have been drained to grayscale by the INKT Corporation.
In Fable III, after the party at Reaver's mansion where he and his guests are unmasked as balverines, the loading screen may show a "Reaver is Industry" propaganda poster with "industry" crossed out and replaced with "a deviant".
A variant is used in Grand Theft Auto: San Andreas; Finding graffitti done by rival gangs and spraypainting the Grove Street logo over it is a good way to build the Grove's respect early in the game.
There is a lot of other resistance graffiti seen throughout the game, besides the lambda symbol. Some of it is somewhat cryptic as to its meaning, but some of it references dystopian novels like Brave New World and 1984.
Delsin in inFAMOUS: Second Son was a graffiti artist before getting his powers. He has a tagging mini-game that lets him screw with the DUP's propaganda by putting up his own art that usually depicts them in a less flattering light (usually something embarrassing in the heroic path and something violent in the infamous path). Sucker Punch art director Horia Dociu says the game's style was largely influenced by Banksy.
This is the premise in the Jet Set Radio games. Rokkaku and his corporation have bought practically all of Tokyo in the future; your player character is a gang leader who sticks his middle finger to Rokkaku by spraying graffiti all over the town.
The Last of Us: The symbol of the Fireflies and the phrase, "Look for the light" can be found graffitied around the game, even in the heavily military controlled Boston.
From the second act of Marc Ecko's Getting Up: Contents Under Pressure onwards, the plot is entirely about this.
The Runners and other anti-government activists in Mirror's Edge mark their caches with graffiti.
In Red Faction, "Eos Lives" can be seen spray-painted on walls throughout the game.
Sid Meier’s Alpha Centauri: Apparent events of cinematics accompanying the completion of "Self-Aware Colony" secret project, include two people fleeing from a "We Must Dissent!" plain graffity, only for them to end up locked in a passage and have something horrible done to them. The almost finished writing is then shown to be removed without a trace within seconds by automatic mechanisms.
In Spec Ops: The Line, anti-US graffiti covers the walls of Dubai, where the local residents come into bitter conflict with the American troops imposing a military regime upon the city.
Some of the Terran Resistance fighters in Exosquad are often seen spraying graffiti onto walls, calling to resist the Neosapien rule.
The French Resistance in WW2 hit on the idea of using the single letter "V" (Victoire) as a defiant gesture against the German occupiers. Also the iconic four notes of Beethoven's Fifth spelt out "V" in morse code (three short notes, one long) and this was used as psychological warfare by both British and French.
A very unpopular and paranoid eighteenth century Pope was plagued by the mysterious graffiti "I.S.S.S.V" appearing all over Rome. It stood for In Settembre Sera Seda Vacante. ("By September the throne will be empty") The paranoid pope became even more paranoid and started to develop symptoms of insomnia and disturbed eating patterns. Sure enough, by the following September he was dead...
The famous "Lennon Wall" in Prague, Czech Republic. Under Communism, western music was banned in Czechoslovakia, but was still often smuggled in. After John Lennon's death, a wall in Prague was covered with graffiti relating to John Lennon. The next day, the wall was whitewashed over. The next night, the wall was covered in graffiti again. This cycle continued many times, and today the graffiti-covered wall is a symbol of youth resistance.
Five hats means that five tropers think it is ready to publish.
You are saying that you think this draft is ready to be published. That means the description is not ambiguous,
it doesn't duplicate an existing trope, there are at least three examples, and the title makes sense.
Is that what you meant to do?
You are saying this draft has a ready-to-publish hat it does not deserve and you are taking it back.