And if the person who hacks your account happens to notice all your posts have a signature and that you said that there is little point. A better safeguard would be to encrypt the date and using a public-private keyset and that way if the date posted and encrypted date are not the same we know it's not you. Just for anyone who doesn't know, this means he can encrypt messages with the private key no one else knows, but anyone can decrypt. That way no one can impersonate him. Of course most people are too lazy for that.