One of the joys of watching Quentin Tarantino films is seeing how he subtly connects each one, creating a loosely unified universe. It's rarely a full-fledged crossover and usually a mention or an Easter Egg of some sort.
Django Unchained is no different, it turns out. Despite being set in the pre-Civil War South, Tarantino subtly worked in a reference to another movie of his - this time Pulp Fiction. Redditor thefirerisesnolan* found the reference, and made this image to help you better understand it: