Watchword

Part of speech: noun (n.)

1. 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.

2. A sentiment or motto; esp., one used as a rallying cry or a signal for action. Nor deal in watchwords overmuch. Tennyson.