] New Yorker Joshua Kinberg is a bike messenger of a
] different stripe. Instead of ferrying legal papers
] between lawyers, he uses a homemade, wireless,
] bicycle-mounted dot-matrix printer to spray protest
] messages in the street.

More digital graffiti. This is a much more practical implementation then the spray paint robot. Unfortunately, this guy got arrested at the RNC.

Wired News: Bike Writer Pedals for Protests