letterhead vs placard

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. 

placard

noun
  • A sheet of paper or cardboard with a written or printed announcement on one side for display in a public place. 

  • A kind of stomacher, often adorned with jewels, worn in the fifteenth century and later. 

  • An extra plate on the lower part of the breastplate or backplate of armour. 

  • The woodwork and frame of the door of a closet etc. 

verb
  • To announce with placards. 

  • To affix a placard to. 

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