Also, John Henry. One's signature, as in Just put your John Hancock on the dotted line. This expression alludes to John Hancock's prominent signature on the Declaration of Independence. The variant simply substitutes a common name for "Hancock." [Mid-1800s]
n. one’s signature. (Refers to the signature of John Hancock, one of the signers of the Declaration of Independence.) Put your John Hancock right here, if you don’t mind.