This is crazy. Dentsu London created an interactive promotion for greentomatocars that uses lasers to sketch murals on buildings. 

The film was shot on a Canon 5D Mark II and uses laser technology to trace transient green illustrations and murals across some of London’s darker corners. The technology was developed by Sensaa.

The Laser Graffiti is a camera and PC setup, tracking a green laser point across the face of a building and generating graphics based on the laser’s position. These graphics then get projected back onto the building with a high-power video projector to complete the illusion.