Yes, either a notary public or a witness should sign your document. Depending on your jurisdiction, notarization may or may not be a requirement. Regardless, signing the document in the presence of a notary public helps reinforce the validity of the agreement. Some banks and institutions have certain signing requirements and may refuse a document that’s not properly witnessed. Notarizing your document often helps avoid bureaucratic hold-ups. Jurisdictions that don’t require notarization may allow a neutral third party to witness the agreement. A witness can be any adult who doesn’t benefit from the guarantee or loan in any way.