Every time this comes up, (a few times a year) I mention that I have bicycle licence plates from the 1950's when you did register a bike. No one seems to know why it stopped. I think the cost of doing it is more than the income that would be generated from small taxes on a bike. The plates I have are smaller and metal with raised letter just like a car plate. They probably cost the same as a car plate to make, the small difference in material used is not much. It's mainly the tooling and the labor. In my state they say prison inmates make the plates, I have no idea if it's true.