The phrase "put one's john hancock on" is an idiom that means to sign a document or a piece of paper. However, there are other synonyms that can be used in place of this phrase, such as "pen one's signature," "endorse," or simply "sign." Other informal phrases that convey the same meaning include "put one's X on" and "make it official." Regardless of the phrase used, the act of signing a document plays an important role in legal and business transactions, as it indicates acceptance or agreement with the terms or conditions outlined in the document.