To show grounds for concluding (that); to indicate, imply.
To have an argument, a quarrel.
To debate, disagree, or discuss opposing or differing viewpoints.
To present (a viewpoint or an argument therefor).
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.