title: Git sign off previous commits?
body: <p>I was wondering how to sign(<code>-s</code>) off previous commits that I have made in the past in git?</p>
  <p>CLARIFICATION: Git has confusingly <a href="https://medium.com/@MarkEmeis/git-commit-signoff-vs-signing-9f37ee272b14" rel="noreferrer">similarly named concepts</a>
  <code>git commit -s, --signoff</code> (lower case -s) and <code>git commit -S, --gpg-sign</code> (upper case -S).<br />
  This question is about signoff(lower case -s).<br />
  However some answers here are about gpg-sign(upper case -S), that better discussed in dedicated questions on superUser <a href="https://superuser.com/questions/397149/can-you-gpg-sign-old-commits#">Can you GPG sign old commits?</a>
  and stackoverflow <a href="https://stackoverflow.com/questions/41882919/is-there-a-way-to-gpg-sign-all-previous-commits">Is there a way to gpg sign all previous commits?</a></p>