https://www.comc.com/Cards/Baseball/...ure,sr,ot,i100
A seller or two have also been selling blank back proofs with no signature on them through COMC.
You can see on this Dale Murphy blank back that the black line around the photo is present, while the signature is missing. Not a true blackless card, but another interesting variation nonetheless.
I think COMC is mis-characterizing the In Action cards (and I've reported it to them) because those cards don't regularly come with the signature. Those should just be listed as blank backs.