That looks real to me. It has characteristics we see on many if not most fast post-2000 McCartney autographs signed on slick surfaces. BTW, this was not signed as a pickguard. It was a sheet of plastic that was cut after it was signed.
I hate that some shady sellers call this a "signed Paul McCartney guitar" when Paul was never anywhere near the guitar. Seems like the latest trend to take a signature or piece of plastic and fashion it into a pick guard.