For U.S. Catholics, Mass for Epiphany is celebrated on the nearest Sunday, January 3 this year. However, like the old Italian ladies in Rocco's neighborhood, some of us like to get our full twelve days of Christmas, and there's no reason you can't participate in some Epiphany customs on the feast day itself, which is, of course, January 6 (Making tonight Twelfth Night, by the by). One of the most prominent among these is inscribing the initials of the Three Kings, along with the numerals of the new year, on your door frame. Now, unless you're making it to daily Mass tomorrow morning, you'll probably have to resign yourself to using unblessed chalk (though, if you are, here's a copy of the blessing for your priest to use).
The USCCB provides a rite for the blessing of a house on Epiphany on their site. Writing on the doorframe could easily be inserted right before the closing prayer. If you still aren't convinced, here are some pictures of chalked doors from around the world* for your inspiration.
Other customs include eating spicy or eastern-style foods, in honor of the Magi, and, of course, King's Cake. More Epiphany customs, as well as further details on inscribing your door, can be found at Women for Faith and Family's site.
*NB: This is a search results page, so the content may change from time to time, including some less-than-relevant photos.