Digital "graffiti" would be purely an imitation of style and tools, though - I'm pretty sure that at least some of the appeal of graffiti is that you're not sup

Digital "graffiti" would be purely an imitation of style and tools, though - I'm pretty sure that at least some of the appeal of graffiti is that you're not supposed to be painting there and could get in trouble for it, and also the fact that it places your mark on a definite bit of physical space. The latter is the only reason I can think of for e.g. tagging.