What's the minimal (not the entire public key) and secure enough way of sharing your PGP key in an email signature?
If you have your publick key on key servers you can only share fingerprint, a link for download your public key is good if you haven't key on key servers or even when you have on key servers because maybe not all people use same key servers.
I use fingerprint and also I have a link to my public key on my blog.
gpg --recv-key B76036EDCAF1C2806B54F51F134C62027E67BBA2
Maybe also you can use key ID and it's possible search on key servers by email and check ID, but it's better to use fingerprint.