Update from the original post: I made a big trade and ended up with a Gossage autograph on a normal-sized baseball card (and frankly, a card I like better than the jumbo one I originally obtained. This works much better for me, and now I have an extra Gossage autograph to trade or sell.
The second HoF signature i found on my recent visit to Randy's Sportscards in nearby Quakertown, was this oversized card of Rich "Goose" Gossage, signed in black marker. Gossage was an incredible pitcher, and I have already had a failed attempt to get his signature through the mail.
The giant baseball card has a bit of a crease, but the signature is clear (if not a bit faded).