letterhead vs posting

letterhead

noun
  • Paper marked with a letterhead. 

  • A portion of text at the top of a letter, identifying the sender and often giving their address etc., used for formal correspondence. 

posting

noun
  • An item inserted into a register, ledger or diary. 

  • The place where a soldier or airman is posted for duty; the time spent there. 

  • A message posted to a computerized bulletin board, a newsgroup, a blog, etc. 

  • The action of the verb to post. 

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