A "testimonium clause" is a phrase in certificate wording in which the Notary formally attests to the truthfulness of the preceding facts in the certificate. A testimonium clause typically appears directly above the Notary's signature. Testimonium clauses may take the format:

"Witness my hand" or "Witness my hand and official seal, this (date) of (month), (year)" or a similar variation. "Hand" refers to the Notary's signature.

Testimonium clauses are not used for certificate wording in every state. In some states, a testimonium clause may not be required for certificate wording if the date of the notarization appears in another part of the certificate.