They represent the muses of tragedy and comedy Thalia and Melpomene. Thalia is the muse of Comedy in greek drama and is shown as a laughing mask and Melpomene is the muse of tragedy and is shown as a crying mask. These muses are the inspiration for creating art forms, such as tragedy and comedy. They are represented as masks because the actors of Greek plays work masks to represent their characters. Now that is the real deal ~Theater Doc. "One of the most common symbols of the theatre are the two masks. The happy-faced one represents comedy, while the sad faced one represents tragedy, the two most common facets of theatre. The mask is the quote-on-quote symbol because when formal "theatre" was first started, the characters used to use masks to indicate emotion." ~Annonymous