Hi Maddstone,
There´s a short film by a guy called Matt McCormick from Portland, Oregon, USA called The Subconcious Art Of Graffitti Removal which puts forward the idea that, while graf itself is a conscious, and often designed, therefore non-abstract art medium, it´s removal by painting over it in large blocks of single colours by government employees has in fact created a new movement of subconscious art... Me, I dunno whether he´s takin the piss or not, but it´s a good little film.