VeloCityLight

I'd buy that for a dollar.

If they really wanted to make a safety device, they should use a camera+ocr+LEDs to shine the number plate of the following car, underneath the words "YOUR REG HAS BEEN RECORDED".

Just like websites that say "Your IP is x.x.x.x and has been logged".

Might make them a little less likely to mow you down knowing their plates have been posted to a server somewhere.

(make it fire rockets into dosy peds and I'll buy one)