Graffiti, fundamentally, is a defacement of public property as a form of artistic self expression. To that end, why not combine this with a laser engraver instead of a laser pointer?
Imagine hooking this up and then literally carving your graffiti into the side of a brick building. Or burning it into the paint on a metal container car.
Obviously such a thing has the potential for serious bodily harm and could start building or wild fires inadvertently, to say nothing of the energy consumption requirements such a laser engraver would necessitate.
Counterpoint: rule of cool.