I've actually made a few of these.
They're totally badass in a DIY kind of way.

Traffic comes to a halt to stare at my wheels.

Setting up the hall sensor to get an accurate readout is a bit of a pain though, and sometimes they glitch out and the image turns into a pile of pixels, only to reappear after a few more revolutions.

Also, I moved the battery packs off the board, so that they can be on the other side of the wheel, to balance them a bit better.

They also require conformal coating if you are ever going to run them in the elements.

Generally I have them programmed with the following bitmaps:






I tried making a good '******' bitmap, but it was too hard to make out on the bike.