To authenticate or verify in writing.
To attest that a product, service, organization, or person has met an official standard.
To attest to (a fact) as the truth.
To add a second signature to a document, affirming the validity of the signature of another person.
To sign on the opposite side of (a document).
A second signature added to a document to affirm the validity of the signature of the first person.
The response to a sign or signal.