Revolution

Revolution turns your bike wheel into a rolling stamp. The stamps are 3D printed letters to clip on your wheel with a cable tie. Push the inking roll against the wheel to ink the letters and leave your message on the pavement. You can easily customize and 3D print all the parts you need.
All the instructions: http://streettoolbox.wikia.com/wiki/Revolution
The message can be customized with this thing:
http://www.thingiverse.com/thing:356902
The current design works on disk brakes and fixed geared bikes. We're currently developing solutions for caliper braking.
Or you know, don't use the back brake, only the front one...

Video: https://vimeo.com/100799128