calling card vs caution

calling card

noun
  • A phonecard. 

  • A card advertising the services of a prostitute. 

  • Excrement, especially of a domestic animal. 

  • A small printed card which identifies the bearer, traditionally presented for introduction when making a social visit to a home or when attending a formal social event or business meeting. 

  • An attribute, symptom, object, or behavior which is distinctly characteristic of someone or something. 

caution

noun
  • A yellow card. 

  • A formal warning given as an alternative to prosecution in minor cases. 

  • Security; guaranty; bail. 

  • Prudence when faced with, or when expecting to face, danger; care taken in order to avoid risk or harm. 

  • A careful attention to the probable effects of an act, in order that failure or harm may be avoided. 

verb
  • To warn; to alert, advise that caution is warranted. 

  • To give a yellow card 

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