If you've tried to commit using SSH keys, you might get this grey icon:
In this post, I'll talk about how to get it to this:
First off, follow Github's guide to generating and linking your GPG key.
However, this might not work. Most likely, this will be because your user email may be different from the one you have on github. Check which email you have on github, and check which email you have on your local git:
git config user.email
And then either change your Github email address, or change your local git email address by:
git config user.email "username@email.com"
Finally, you can push signed commits to Github by:
git commit -S -m "Blah blah commit"
Voilà! Hopefully this works for you.