I have a 1988 Topps (759) card that was signed by Mark McGwire & Jose Canseco in Oakland almost 20 years ago. My older brother got them to sign it while they were warming up before a game. This card is in mint condition and there is a slight/faint thumb print mark on Mark McGwire's signature. The signature is not smudged. My brother and I think it is Jose's print because Mark signed it first. What would the approximate worth of this card be?

I found one on the following site that is number 759.

Autographed Jose Canseco Topps #759 Baseball Card 1988 - eBay (item 170208635627 end time Apr-13-08 20:00:02 PDT)

The ending bid was $24.99. With a couple of autographs on the card, it should be worth something more than that.