The first bit of graffiti I ever laughed at was on the men's room wall at a san francisco retail store. "Krishna Saves".

There's also a local artist who's done a series of 'signs' that, although not graffiti, are worth mentioning. His standard format is the black and white highway information sign, done huge. Three stories high, pointing up 'SKY'; 75 feet across, pointing at a large tree 'ONE TREE'. It's better in person.