With all due respect to Mark, but I think he solved the problem that he created himself. He signed random Squiers, scratch plates, and whatnot, he signed guitars that his manager brought to him after collecting them from fans. He signed instruments purely at random, and after that, who would've thought, they ended up on eBay.
He tried to ask people at least to play something before signing, but that would only eliminate a small portion of Rüdigers. Nobody really knows if the person who asks you to sign a guitar is a genuine fan or a genuine fake guitars trader, so in all honesty, I think it's a pretty good decision. I think if you really, deeply want a guitar to be signed by Mark, you can try to approach it through managers or so, I think with a really good story or attitude it is still possible to get a signature. It's just he won't sign guitars at random like before.