This looks really interesting.
“Two documentary filmmakers set out to expose a prolific anti-graffiti vigilante vandal who spray-paints silver blobs over existing graffiti. Through trial and error, the filmmakers hone their amateur surveillance skills and eventually identify and confront their target. The film then ventures deeper into questions over the legitimacy and motivations of graffiti and anti-graffiti, with perspectives from both sides and examples of three other well-known anti-graffiti vigilantes across the US.”
More info: http://www.vigilantefilm.com/