check in vs sign on

check in

verb
  • To announce or record one's own arrival at a hotel, airport etc. 

  • To verify a person's information and record their arrival, such as at a hotel, airport, etc. 

  • To integrate new revisions into the public or master version of a file in a version control system. 

  • To visit in order to see how someone is doing. 

  • To contact another person in order to keep the other person informed of one's situation. 

  • To return (a book to a library, source code to a repository, etc.). 

  • To enter solitary confinement at one's own request for protection from other prisoners. 

  • To send somebody to solitary confinement; to make somebody be admitted to solitary confinement. 

sign on

verb
  • To join something, after signing. 

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

  • 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 check in and sign on occurred in a corpus of books? (source: Google Ngram Viewer )