application/pgp-signature

An OpenPGP signature.

Extensions
.asc .sig
Header
Content-Type: application/pgp-signature
Registered
Yes, in the IANA media type registry.
References
IANA · RFC 3156 · Apache

What servers send

The type each server's own mime.types gives these extensions, as it ships.

ExtensionApache httpd 2.4.69nginx 1.31.6
.asc application/pgp-signature Not listed
.sig application/pgp-signature Not listed

The IANA registry also gives these extensions to application/pgp-keys and application/rpki-checklist.

Common application types

Every media type, in one table