LED Graffiti In a Can
"Halo is a handy light-writing tool, preserving the techniques and gestures that graffiti artists use with spray cans. It is possible to change the color and the brightness of the led to change the graffiti's styles. If the light doesn't have enough battery, users simply have to shake it to have energy again."
Scroll all the way down for a How-To employing a similar technique.