Ask and you shall receive, Barry. Here is Louis Weichmann's signature:
I think both you and Laurie are absolutely correct about the Nothey letter being written by Weichmann. Here is the Nothey letter signature again, along with a part of a letter Weichmann wrote to Col. Burnett while he was imprisoned. In the letter he writes additional facts that he wishes to attach to his previous statements. He wrote "Mrs. Surratt" many times in this letter:
Weichmann letter to Burnett:
These two look like the same hand to me. Good catch, Barry.
I also think one of the signatures I put up for John Surratt Jr. is probably the signature of a secretary at the Baltimore Steam Packet company instead. Blaine provided a bold handwritten letter and signature from 1901, which is quite at odds with the 1908 signature at the end of a typed letter that I previously found.
I don't think the 1908 one is genuine.