[Exhibitman]

No, that's incorrect.

American Heritage Dictionary: "A person's own signature or handwriting"
Merriam-Webster Dictionary: "a person's handwritten signature"
British English Dictionary: "a signature (= your name written by yourself) of a famous person"

Lewis stood in front of me and signed my card in his own hand = autograph. Sloppy doesn't come into the equation. If it did there would be practically no autographs of modern day baseball players!