motto vs watermark

motto

noun
  • A sentence, phrase, or word, forming part of an heraldic achievement. 

  • A sentence, phrase, or word, prefixed to an essay, discourse, chapter, canto, or the like, suggestive of its subject matter; a short, suggestive expression of a guiding principle; a maxim. 

watermark

verb
  • To mark paper with a watermark. 

  • To mark a datafile with a digital watermark. 

noun
  • A mark indicating the level to which water has risen. 

  • A translucent design impressed on the surface of paper and visible when the paper is held to the light. 

  • A logo superimposed on a digital image, a television broadcast, etc. 

  • A value stored in a datafile to ensure its integrity, so that if the file's contents are changed then the watermark will no longer match the contents. 

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