What does `sig!3' mean in the output of `gpg --check-sigs'?

[Eric Hanchrow]

In particular, what do the exclamation point and the 3 mean?  As you
might guess, I checked all the documentation I could find, and even
looked at the source (which wasn't illuminating).
-- 
"New York Minute" is a textbook example of a film created as
a "vehicle" but without any ideas about where the vehicle should
go.
        -- Roger Ebert