As a user, I noticed my usual .sign files where not reported as an application/pgp-signature type when fetched from my web server. In this scenario, the actual detached signature file of a PDF, i.e with a .pdf.sign extension, was simply reported as a application/pdf until I modified as a test on the server its /etc/mime.types file to consider those sign extension. It was successful, or at least how I expected.
By experience I see more "sign" as a contraction for "signature" than "sig", for example as the CLI arguments and options of GnuPG.

I am not sure if this is the right approach to this usage. I later discovered the IANA’s Media Types list after I started to create those commits. I understand if this is not the correct approach to this project and therefor if you decline this PR.