[Leon]

I have followed autograph auctions for at least 15 yrs, due mainly to being in the card hobby, so have seen several "alleged" Joe Jackson type autos. I might be wrong, but I don't remember ever seeing one where he signed (of course he was somewhat illiterate, to what extent is debatable) only a J. That being said, to me, those exemplars of Js don't look like the one on back of the card.

If it were me I would consider it a neat card, use it for my type from that set, and feel like it has a lightly erased mark on the back. The mark would be completely inconsequential (to me).