epigraphy vs graffiti

epigraphy

noun
  • The study or decipherment of inscriptions, especially of ancient ones. 

  • Inscriptions collectively. 

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 epigraphy and graffiti occurred in a corpus of books? (source: Google Ngram Viewer )