I have a Rickenbacker bass that is personally autographed by John Entwistle (and Chris Squire as well). I must say that the signature looks pretty authentic, from my amateur eye.
I could never bring myself to sell my bass. How could I get rid of a bass guitar that is autographed by the two people who are responsible for me ever wanting to purchase one? There's no way, I'm never going to get one again
Now if I could only get Paul McCartney to sign it