I think people who go around tagging buildings with spray paint should suffer some kind of humiliating punishment, but I might change my tune if more of them were like this artist called Mudlevel.

His Robo-Rainbow paints a perfectly formed multicolored rainbow on any wall in about 15 seconds, using a giant mechanical sweep arm loaded with spray cans. The device is surprisingly complicated, with an Arduino processor controlling an electric drill, and servos to trigger the spray can nozzles.

The 15 second painting time should give you plenty of time to escape, but I think riding that huge rig down the road will tip off the cops about your plans.

Hack-A-Day, via Crunchgear