Signature, in this title, means the name of the party, written by himself; as evidence of his assent to an instrument as a party, or to attest it as a witness: the family name must be written at length—the baptismal or prenominal name may be abbreviated, or indicated only by the initial letter, or altogether omitted, if such has been the usual mode in which the signer has subscribed his name.
Source: wiktionary