Iphone 4S Text Message

When I go to create a "new message," the text box already has text from an old sent message. How do I delete it permanently?

 

It just shows up the next time I try to send a new message. It returns like a signature, but texts don't have a signature option, right?

 

Yes, twice. I've plugged into itunes to see if that made a difference. I've thrown it across the room and called it all sorts of horrible names and nothing!