Who is the big bad graffito — all of those automobile tailpipes or the guy scrubbing soot off the wall of this tunnel in Sao Paulo? A Streetsblog tipster sends along news about a cool new urban art form:

A number of street artists around the world have taken to expressing themselves through an innovative practice known as Reverse Graffiti. Taking a cue from the "Wash Me" messages scrawled on the back of delivery trucks, they seek out soot covered surfaces and inscribe them with images, tags, and even advertising slogans using scrub brushes, scrapers and pressure hoses.

Brazilian Alexandre Orion, turned one of Sao Paolo’s transport tunnels into a stunning mural last summer. The mural, comprised of a series of skulls, very succinctly reminds drivers of the impact their emissions are having on the planet.

The authorities were 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.