Watchword

[Britney]

A word given to sentinels, and to such as have occasion
to visit the guards, used as a signal by which a friend is known from
an enemy, or a person who has a right to pass the watch from one who
has not; a countersign; a password.

[Becky]

–noun

a word or short phrase to be communicated, on challenge, to a [sentinel] or guard; [password] or countersign.
a word or phrase expressive of a principle or rule of action; slogan: Conservation has been our watchword.
a [rallying] cry of a party, club, team, etc.

[Renato]

A word or phrase expressing a person