The link for the customizable stamps can be found here.

http://www.thingiverse.com/thing:356902

First you will need to register on Thingiverse.

Then click the "Open in Customizer" button at the right hand side.

Enter the letter, number or sign you want in the text box.

Click "Create Thing" button at the lower right corner. Click "Create Thing" button in the message box again.

Download the stl. file in "My Thing" of your Thingiverse account.

You can then print you stamps with the Ninjaflex material. I found that a max speed of 40mm/min was giving the best results with this material.

Now it's time to mount them on you wheel with some cable ties.

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...