http://GraffitiResearchLab.com
"In its simplest form the Laser Tag system is a camera and laptop setup, tracking a green laser point across
the face of a building and generating graphics based on the laser's position which then get projected back
onto the building with a high power projector."
Watch the video:
http://www.youtube.com/watch?v=DKbtTPYZEig
Xantherus