catchline vs watchword

catchline

noun
  • A short line of text designed to catch the eye, especially one used as an advertising slogan. 

  • A temporary note at the top of a page or galley proof to identify it. 

watchword

noun
  • A word used as a motto, as expressive of a principle, belief, or rule of action; a rallying cry. 

  • A prearranged reply to the challenge of a sentry or a guard; a password or signal by which friends can be known from enemies. 

How often have the words catchline and watchword occurred in a corpus of books? (source: Google Ngram Viewer )