To certify by signature or oath.
To affirm to be correct, true, or genuine.
To certify in an official capacity.
To put under oath.
To supply or be evidence of.
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.