Signatory
/ˈsɪɡ.nə.tɔː.ɹi/
noun
One who signs or has signed something.
“John Hancock is famous for being the first signatory to the American Declaration of Independence, and for writing his name large.”
Synonyms: signer
adjective
Relating to a seal; used in sealing.
Signing; joining or sharing in a signature.
“signatory powers”