·adj A private signal, word, or phrase, which must be given in order to pass a sentry; a watchword.
II. Countersign ·adj The signature of a secretary or other officer to a writing signed by a principal or superior, to attest its authenticity.
III. Countersign ·vt To sign on the opposite side of (an instrument or writing); hence, to sign in addition to the signature of a principal or superior, in order to attest the authenticity of a writing.