-- '%G?': show "G" for a good (valid) signature, "B" for a bad signature,
- "U" for a good signature with unknown validity and "N" for no signature
+- '%G?': show "G" for a good (valid) signature,
+ "B" for a bad signature,
+ "U" for a good signature with unknown validity,
+ "X" for a good signature that has expired,
+ "Y" for a good signature made by an expired key,
+ "R" for a good signature made by a revoked key,
+ "E" if the signature cannot be checked (e.g. missing key)
+ and "N" for no signature