Press Record.

The "PixelRoller" project is a collabortive investigation into a new creative tool between Stuart Wood MA (RCA) Interaction Design and Florian Ortkrass MA (RCA) Design Products.
PixelRoller is a paint roller that paints pixels, designed as a rapid response printing tool specifically to print digital information such as imagery or text onto a great range of surfaces. The content is applied in continuous strokes by the user. PixelRoller can be seen as a handheld “printer”, based around the ergonomics of a paintroller, that lets you create the images by your own hand.
http://random-international.squarespace.com/pixelroller-overview/
Actually the whole site is pretty kick ass, check it out.

JaySay: reminds me of this:http://news.bbc.co.uk/1/hi/technology/3045158.stm only way way cooler.

edit: also see this, bike/SMS powered spray messages:http://www.bikesagainstbush.com/blog/about.php