No, it's a separate feature from encrypting and decrypting. Your PGP program should have a "sign" button or menu option. Take a look at the GPG4USB tutorial linked in my signature. It tells you how to do it in that program. There will also be a "verify" option. One person signs a message and everyone else verifies it with his public key. The purpose of a signature is that it proves whoever owns that PGP key wrote it. It has actually been useful in this community. DPR usually signs his messages so the community can trust his announcements. Also, there was a case where a vendor's SR and forum accounts got hacked. He had to create a separate forum account, and he was asked to post a signed message that could be verified with the public key on his profile, to prove his identity. If you've never messed with signing and verifying, grab my public key from the link my signature and verify this message: Astor wrote this message.