Here is a scan of a W514 Joe Jackson that I own.
On the back there is a single, script "J" written in (what looks like) pen that appears very old given the fading and dirt over the signature and the rest of the card.
Could this have been written by Shoeless Joe himself?
Although he was illiterate and his wife mostly signed for him, there are a scarce few examples of his authentic signature (see scans below).
And being that he
was illiterate, if he was going to sign an autograph for a fan on a small strip card, would it be far fetched to think that he would sign only "J"?
Was he ever known to sign just a "J"?
I guess my real questions is: If this was your card, what would you do?

Authentic and verified Shoeless Joe signatures: