initials vs logotype

initials

noun
  • An abbreviation of a person's name, constructed by taking the initial letters of first, last, and sometimes middle name(s). See monogram 

logotype

noun
  • A symbol or emblem that acts as a trademark or a means of identification of an institution or other entity, usually referred to as a logo. 

  • A single type combining two or more letters (as a ligature or otherwise). 

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