danger signal vs foghorn

danger signal

noun
  • A signal set at danger and showing a red light or other stop indication, which a train driver must not pass until it changes or until manually cleared past the signal by a dispatcher. 

  • An indication that a potentially bad or dangerous situation could develop. 

foghorn

noun
  • A very loud low-pitched horn, used especially in lighthouses and on large boats. 

  • A strong gossiper. 

verb
  • To shout or bellow in a loud, deep voice 

  • To sound a foghorn 

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