Of all art, graffiti probably has the widest discrepancy between the off-handed-ness of its creation and the intensity of the art theory surrounding it. So it's no surprise that added to the mountains of academic papers and discussions is a movement to catalog and organize its slap-dash squiggles. Which, of course, leads only to one thing: Robots.
Graffiti tech has grown like crazy in the last few years, spurred on mostly by the Graffiti Research Lab (check out their EyeWriter project, and the various laser-tagging rigs they've developed. You might have seen one at MoMA.). Then there's Jurg Lehni's spray-painting robot Hektor, another spray bot called GraffitiWriter, and now this.
Free Art and Technology, the umbrella organization that spun off the Graffiti Research Lab, just released GML, an XML language to code--and therefore endlessly reproduce--tags by capturing motion data. Ever since, there's been a flood of new projects using GML posted to FAT's blog--check em out, or go to 000000book.com to dig through hundreds of GML files of different tags.
One of the best applications is Robotagger, by Golan Levin and Jeremy Ficca, two professors at Carnegie Mellon. They rigged up an ABB IRB-4400 robot arm with a fatty Sharpie and plugged it into the 000000book database--instant graffiti machine. No workshop wall is safe!