Reverse Graffiti

"When is cleaning the sidewalks a crime? When you’re doing it to create art. Obviously. […]
The authorities were certainly miffed but could find nothing to charge him with. They had no other recourse but to clean the tunnel — but only the parts Alexandre had already cleaned. The artist merely continued his campaign on the other side of traffic. The utterly flummoxed city officials then decided to take drastic action. Not only did they clean the entire tunnel but also every other tunnel in Sao Paulo."

http://muhh.soup.io/post/1059791

http://blog.koehntopp.de/archives/1991-Reverse-Graffiti.html

http://www.youtube.com/watch?v=JwsBBIIXT0E