The Graffiti Research Lab - "dedicated to outfitting graffiti artists with open source technologies for urban communication" - has a unique form of temporary high-tech graffiti they call laser tagging that utilizes a laser pointer in lieu of paint, a projector in place of a spray. Instead of hitting dark subway tunnels and back alleys, they turn their attention to public places such as skyscrapers and monuments.

The Graffiti Research Lab has great resources including a HOW TO ( and source code) for those interested.

ps: laser pointers are banned in certain places.