Apparently the latest in random city beautification techniques is LED throwies, LED lights taped together with a battery and a magnet which can then be tossed onto any magnetic-friendly metal surface. The delighfully-named Graffiti Research Lab claims credit for developing them, and provides detailed instructions on how to create and use these glowing little bundles of colour.
The New York Times recently published a feature on the Lab. It also recently published a remakably extended and detailed history of traditional graffiti in New York in the words of those who were involved in its creation, diffusion and suppression.