Agreed. I don't believe this is authentic. McCartney usually sticks to the rule of no other items at these kind of signings. There's always a chance he broke away from the rule, but I highly doubt it...not to mention this looks like some other forgeries I've seen posted online. Sorry!
I try not to pay attention to the story, and just focus on the merits of the signature. there could be many reasons why this signature is so non-conforming, but the one thing that I can not get past is the spacing in Paul. I dont think I have seen an authentic one with that kind of space between the a and u. it just looks bad.