defacement vs graffiti

defacement

noun
  • A symbol added to a flag or coat of arms to change it or make it different from another. 

  • An act of defacing; an instance of visibly marring or disfiguring something. 

  • An act of voiding or devaluing; nullification of the face value. 

graffiti

noun
  • Informal inscriptions, figure drawings, etc., as opposed to official inscriptions. 

  • Drawings or words drawn on a surface in a public place, usually made without authorization. 

verb
  • To mark a surface with such images. 

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