I'm using gpg 1.2.4. When I checked signatures on my own key, I've
found that one of my self-sig is marked as "sig!3". What does this
mean? A valid v3 self-signature?

This new user id as well as the self-sig was generated by gpg 1.2.4,
while the other user id was generated by PGP 7 and has a self-sig
marked as "sig!" only.

Does GPG generate a v3 self-sig by default when no expiration date is
specified? Or did I indicate this in options?

This is my gpg.conf file:

keyserver ldap://keyserver.pgp.com
digest-algo RIPEMD160
compress-algo 2
load-extension d:\utility\gnupg\idea
charset utf-8

Thank you.

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While truth is beauty.