Bill Stewart wrote:

If you're concerned about Bad Cops planting forged messages on people, this won't help - it's easy for them to forge unsigned information also. After all, the PGP source code is open, so Bad Cops can add code to set the timestamp/sender/etc themselves. Or they can ignore code, and just set their system clock appropriately.

BC's can also plant secret keys on your machine, along with messages forged using those keys. It is a good idea to keep badly forged messages on your machine, as well as badly forged keys. There are many ways to manipulate files and emails so that discrepancies exist. e.g. - messages with a time-stamp later than the file date; replies with an earlier time-stamp than the original message; changing fingerprint on the same key.