OK, now it gets weird. The "JSA Auction Letter" turns out to be a full JSA LOA. The item, sadly, is a preprint. Here is the one I already own (top card):
Unless Jim Jeffries managed to sign these cards with identically placed and sized signatures, right down to the spacing of the loops between the letters, this is a preprint that JSA certified as an autograph
with its full LOA, after being "thoroughly examined."
Really???
ETA: I do have to clarify one thing: the 'signature' is an overprint, not a watermark. Regardless, it ain't signed. I think I'll contact JSA...