The actor is the ultimate sign system. Through the body alone the actor can tell thousands of stories through his/her actions.
I know of three which helped me for my dissertation. 'Theatre as Sign-System', Elaine Aston and George Savona. 'The Semiotics of Theatre and Drama', Keir Elam. 'The System of Objects', Jean Baudrilland. Hope this helps :)
Thanks, I think I have one of them somewhere. :)