Evolution shows "Valid signature, cannot verify sender" for a message
signed by a revoked key. It would be better to make it more obvious
that the key has been revoked -- it may be that the key was compromised
and that signatures from it should definitely *not* be trusted.
In this case, clicking on the 'seal' icon shows warnings from GPG,
including
"gpg: WARNING: This key has been revoked by its owner!
gpg: This could mean that the signature is forgery.
gpg: reason for revocation: Key has been compromised"