Several years ago, another forum I belong to was planning one of our annual club cars, and we toyed with the idea of using some graffiti. We did some research to see just how far back the (art form) went. One example, although not true graffiti is the Kilroy was here markings, which were inspection markings during WWII. An overwhelming majority of members rejected the idea of putting any graffiti on the proposed club car with strong opinions opposing it.
Graffiti, if we define it as any type of writing on the wall goes back to ancient Rome, and if drawn images count, then we could point to the first graf artists. But the style of urban graffiti that most people have seen and know about, the kind that uses spraycans, came from New York City in the late 1960s, and was born on the subway trains. Taki 183, who lived on 183rd street in Washington Heights, worked as a messenger who traveled all throughout the city. While he did so, he would use a marker and write his name wherever he went, at subway stations and also the insides and outsides of subway cars. Eventually, he became known all throughout the city as this mysterious figure. In 1971, he was interviewed for an article by the New York Times. Kids all over New York, realizing the fame and notoriety that could be gained from "tagging" their names on subway cars (that traveled all over the city, naturally) began to emulate Taki 183. The goal was to "get up" (using the slang of the day), to have one's name in as many places as possible, and as kids competed against each other to get famous, the amount of graffiti on trains exploded.
A friend of my son who came to PA from California was a "tagger", and he and some of his friends were caught and fined. The irony is that he was later hired to paint murals on down town buildings. He did a cylindrical hopper for my son with his tag WIKA.