The Collaborative International Dictionary of English v.0.48:
Signer \Sign"er\, n. One who signs or subscribes his name; as, a memorial with a hundred signers. [1913 Webster]WordNet (r) 3.0 (2006):
signer n 1: someone who can use sign language to communicate 2: someone who signs and is bound by a document [syn: signer, signatory]