Andrew,
I collect Bresnahan cards, and I have seen numerous contracts in auction houses with his signature. It's possible that he may have signed with a pencil which wasn't unusual back in the day. With that being said, I'd lean towards not original. Bresnahan's signature is pretty legible on the contracts I have seen listed.
http://www.lelands.com/auction/Aucti...igned-Contract
http://feb13.hugginsandscott.com/pl/..._bresnahan.jpg
Patrick