This guide above pretty much says it all, but i will add that signing works through PGP encryption. You could learn about that because u can sign message without bitcoin involvement at all.
Can you post a link where PGP encryption is being discussed like the thread created by Shorena
There is no such thread yet. I was asked several times to create something similar for PGP, but I have not done anything yet. Maybe velkro wants to create a PGP how to? I dont know.