1) Affirmer 2) Attestator 3) Attestor 4) One who bears witness 5) Signatory 6) Signer 7) Witness 1) Attestator 2) Attester 3) Attestor 
attestant 1. Someone who affirms or vouches for the correctness, or truth, or genuineness of something. 2. A person who attests to the genuineness of a document or signature by adding his/her own signature.
attestor noun (law) a person who attests to the genuineness of a document or signature by adding their own signature