Check out the building in the top photo — it possibly has the largest graffiti tag ever on a building.
But, it also had hundreds of other tags on its side that night. Dutch multi-media artist Huib Van Der Werf hooked up with the Graffiti Research Lab and created this WMD — weapon of mass defacement. Simply put, you can project light on to a surface, in combination with a laptop, some kind of open source software, and a hand-held laser pointer, that creates the illusion of writing or drawing anything you want onto the side of a building. The photo above is the apparatus created for this project.
You can find out how to do it by going to this website. Also, check out the video on You Tube which shows the WMD in action.