log off vs sign on

log off

verb
  • Synonym of log out. 

  • To depart from any conversation, online or in person; to say goodbye. 

sign on

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

verb
  • 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 join something, after signing. 

  • To apply to receive unemployment benefits. 

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

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