To sign on the opposite side of (a document).
To add a second signature to a document, affirming the validity of the signature of another person.
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.
to write on the exterior of, the surface of, or above.
To address (an envelope etc.).
to write (something) on the exterior of an object, such as a document or an envelope.