disapprove vs sign off on

disapprove

verb
  • To have or express an unfavorable opinion. 

  • To condemn; to consider wrong or inappropriate; used with of. 

  • She disapproves of rap music because of its sometimes aggressive lyrics. 

  • To refuse to approve; reject. 

sign off on

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