[Twinfan]

I have a private plate on my bike, and the missus does on hers. They're not bike specific though in what they say, so can be transferred to other bikes. I think car/bike specific ones are a bit daft. Personal plates e.g. initials make much more sense.

So I voted "Yes", but reading your example of "SS FE" I would say don't bother. I think that one sounds pants.