If there's no ownership make sure you call a police station and ask them to run the VIN to make sure it's not stolen.
This.
There are plenty of other things you can do to document that you own the bike.
If the VIN has been altered or removed then there's a good chance that it's fishy. If there is a VIN but no ownership there are plenty of legitimate reasons for this that would not make it fishy IMO. My 10R has a valid VIN but no ownership. Lots of folks build up salvage bikes into race or track bikes and for most there isn't much point in getting an ownership so why bother?