You can also have fun by tagging arbitrary objects in git:
[...] you can tag any Git object. In the Git source code, for example, the maintainer has added their GPG public key as a blob object and then tagged it. You can view the public key by running this in a clone of the Git repository:
git cat-file blob junio-gpg-pub
https://git-scm.com/book/en/v2/Git-Internals-Git-References