dollar sign vs greenback

dollar sign

noun
  • The symbol $, used to indicate a price in dollars. 

greenback

noun
  • The United States dollar. 

  • A unit of American currency issued during the Civil War by the Treasury Department. 

  • A wave that has not yet begun to break. 

  • Any bill that is legal tender in the US (originally printed with green and black ink) issued by the Federal Reserve. 

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