Nickname for Modesto, California, so named because George Lucas based the script for American Graffiti upon events that occurred there during his senior year at Downey High. He just changed everyone's and everything's names enough so they couldn't sue him for defamation of character.
Modesto also used to host the biggest Graffiti Night rallies for a few years after the movie came out.
Q. Where you from?
A. Graffiti City.