I am looking at buying a motorcycle but the one i would like has no registration number?

You might be buying a heap of trouble. Current owner should have a title that can be signed over to you. If not,don't buy. If you do anyway, get ready to spend a lot of money to straighten out the title mess. The bike may be stolen or it could have been built up from salvage parts. In any event it must have a number to be registered even with a salvage title. r