Well, I suppose it isn't that difficult to sign in third person. Just begin every sentence with a spelling of your name. Or, if I were to go under the name "Bunny" in real life, which I don't, but if I were to use it, I would just use the 'word' for 'Bunny' before every sentence.
I'm not really mute. Although I have been known to just not talk for days on end.