The same seller has this Grover Cleveland Alexander, which looks too good to be true. I don't know enough about his signature nor Tinker's, but I do know that B&W Plaques are highly forged and most of the real ones I've seen don't look as though they were kept in a vault for years. I'd be leary.
http://www.ebay.com/itm/GROVER-ALEXA...item4acd5f1b1b