Watchword

Noun

 * 1) a prearranged reply to the challenge of a sentry or a guard; a password or signal by which friends can be known from enemies
 * 2) a word used as a motto, as expressive of a principle or rule of action; a maxim, byword
 * 3) * 1919, Boris Sidis, The Source and Aim of Human Progress:
 * Atrocities of the most vicious kind were justified by the watchwords: "This is war!" "Might is Right." "Necessity knows no law."
 * 1) a rallying cry

Thesaurus
bugle call, byword, call to arms, call-up, catchword, clarion, clarion call, conscription, countersign, device, epigraph, epithet, exhortation, go for broke, gung ho, inscription, levy, mobilization, motto, muster, open sesame, password, phrase, rally, rallying cry, rebel yell, recruitment, secret grip, shibboleth, slogan, tag line, tessera, token, trumpet call, war cry, war whoop, word

Etymology
From waccheword:, morphologically as.