Signed messages are never part of a transaction and never added to the blockchain.
The client has the ability to sign any arbitrary text. Once again this has absolutely nothing to do with transactions.
Thank you! Now I understand.
I don't (fully) understand. I just found ''sign message'' and ''verify message'' in Bitcoin-Qt.
Can someone explain in plain English how both differ?
Does ''signing / verifying a message'' involve paying a TX fee?