The boost repository requires DCO signing. By adding a signed off line to your commit, you verify the following, Developer Certificate of Origin.
You can add the signed off line to your commit by adding the -s flag to the git commit command.
If you'd like to automatically sign off all of your commits you can add a prepare-commit-msg hook to do so. A good example can be found in the Git prometheus repository DCO wiki entry at the bottom of the page.