Neither of these are authentic. I would extend that opinion to all of this seller's BTTF signatures. This seller has been discussed several times in different forums (including here recently) and the opinion is never good. I would stay away from this seller.
don't know the story of this seller but a autograph on a delorean car is hard to authenticate but can't find anything wrong on the Lloyd. could be done by a great artist because you have to sign it in one time?...if there is no photo proof of signing and a coa that matters than JIM G could be right to stay away...