Apparently they're really popular. Hallmark started producing the green-themed cards back in the early 1920s. They now offer more than 100 cards dedicated to the holiday. There's the one of a Dalmatian covered in four-leaf clover instead of black spots. It reads, "On St. Patrick's Day, everybody's Irish." There's also an e-card with a dancing mug of green beer set to Men Without Hats' "Safety Dance." Hallmark says 12 million Americans exchange St. Patrick's Day cards each year. The company's sales are highest in the Northeast, with New York City topping the list.