The crossword solution for the term 'certify, as a signature' is 'notarize'. Notarizing is a process in which a notary public, an official appointed by the government, witnesses the signing of a document and verifies the identity of the signer. The notary public then signs the document and adds their own seal or stamp, certifying that the signature is genuine. This process is often used for legal documents such as wills, deeds, and contracts.