A link I posted about the origin of emoticons has elicited quite a few pointers to prior artwork. The first being the Plato computing system which appeared in 1972, a decade before the ASCII emoticons of CMU. Even more interesting, The Register has an unconfirmed report of emoticons on punch tape and punch cards back in the 60's. I expect this battle to go back to Turing representing a smiley on one of the Bombes at Bletchley Park.

Thanks to Nathan and Timmer among others.