a human being

be engaged by a written agreement

mark with one's signature; write one's name (on)

engage by written agreement

approve and express assent, responsibility, or obligation

one of two or more signers of the same document (as a treaty or declaration)

a signer in addition to the principal signer (to verify the authenticity of the principal signature or to provide surety)

a signer of a 1679 address to Charles II in which those who petitioned for the reconvening of parliament were condemned and abhorred

a person who transfers his ownership interest in something by signing a check or negotiable security

(law) a person who attests to the genuineness of a document or signature by adding their own signature