Reverse graffiti is a innovative form of street art with close ties to environmental activists. At most reverse graffiti requires the use of a stencil and a pressure washer, or could use as little as one's finger. This type of graffiti, is less a type of graffiti and more a social service, it involves the cleaning of a dirty surface to form an image. This type of graffiti has close ties to Environmentalists because it calls to attention the pollution that caused this surface to get to the point its at, being caked with dirt and soot to the point where it can be scraped off with a fingernail, as well as providing some perspective on how bad pollution really is by witnessing how fast the clean graffiti is "washed" away naturally by the pollutes and dirt. Much of this graffiti can be seen as advertisements for environmentalists groups sprayed onto the sidewalk, but others continue use it as an art form.One of the "O.G.'s" of reverse graffiti is Paul "Moose" Curtis, who uses a wire brush and detergent. Many cities still treat this graffiti like how they do the rest, as defacing public property, Moose claims that it is refacing as opposed to defacing. Having been accused of breaking the law because of his reverse graffiti, moose brings up an excellent question.Do they not like people cleaning their walls or do they just have a problem with expression?