Graffiti Research Lab is a high tech group dedicated to "outfitting graffiti artists with open sourced technologies for urban communication". What does that mean? High Tech Graffiti! According to Graffiti Research Lab, "LED Throwies are an inexpensive way to add color to any ferromagnetic surface in your neighborhood. A Throwie consists of a lithium battery, a 10mm diffused LED and a rare-earth magnet taped together. Throw it up high and in quantity to impress your friends and city officials." They also have a Flikr group where you can see lots of high tech graffiti. The "Bush Juice" graffiti picture is on a piece of oil processing equipment.
You can find out how to make your own LED Throwies at Instructables, a site we featured a couple weeks ago.