Following up on the slack discussion on doing the DCO signoff on past commits, here's what has been recommended by Steve Winslow as an acceptable way of signing off past commits.
1) Run this command from the main directory in the repo to create a text file with all commits made by you without a DCO signoff ( substitute your information in place of the text in braces )
git log --oneline --committer "<YOUR NAME/EMAIL>" --grep "Signed-off-by" --invert-grep > <INITIALS>_prior_commits.txt
2) Add the following text to the top of the created file by the prior command
The following commits were made pursuant to the Developer Certificate of Origin, even though a Signed-off-by: was not included in the commit message.
3) Commit this back to the repo
git commit -s -m "Signoff for prior commits made without a DCO signoff"
4) Push this back up to Github