OK - here's the thing. I don't mind Graffiti if it is tasteful, colorful, and nice to look at. I realize that it is on public property and it's illegal - but I don't get too worked up about it.
But when I drive by a bridge and see the picture of a giant penis . . . well, look. I live in a house with two boys and a husband. I see my fair share of penises every day whether I like it or not. The last thing I want to look at when I drive under the overpass is the picture of a giant penis with balls not to scale.
Seriously people, stick to 'Grad insert year here' for goodness sake.