appoint vs sign on

appoint

verb
  • To equip (someone) with (something); to assign (someone) authoritatively (some equipment). 

  • To name (someone to a post or role). 

  • To set, fix or determine (a time or place for something such as a meeting, or the meeting itself) by authority or agreement. 

  • To fix the disposition of (property) by designating someone to take use of (it). 

  • To furnish or equip (a place) completely; to provide with all the equipment or furnishings necessary; to fit out. 

sign on

verb
  • To commit oneself, as to a project, a goal, an organization, a cause. 

  • To begin broadcasting a radio or television signal, usually at the beginning of a broadcasting day and after being off the air for several hours. 

  • To join something, after signing. 

  • To apply to receive unemployment benefits. 

  • To log on; to start using a computer, radio, etc., or to start talking. 

noun
  • The time of day when a radio or television station begins broadcasting, usually after being off the air for several hours. 

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