It changes that little smiley that comes up next to your name. Of course it is totally useless as a record of how you felt when you made any particular post in the past since it changes all your little smilies for any post you have made in the past. My advice is just ignore it. The one I have chosen doesn't seem to say much at all so I guess I'll keep it. Unless someone can tell me it means something that is totally inappropriate. In which case I still probably won't change it, but, hey!