Visual artist, Alexandre Orion, executed a technique known as reverse graffiti to fill a tunnel in Sao Paolo, Brasil with his skulls.  On top of functioning as an urban art piece, the skulls are a reminder to those that drive through the underpass of how pollution is affecting us as a whole.  The imagery and message is simply amazing.  The question is how can this be considered vandalism when the artist is reverse graffiti is pretty synonymous to cleaning?

Image Source: Alexandre Orion