Most stations west of the Mississippi have call letters which begin with "K." However, WDAY was licensed before the U.S. government changed its assignment of call signs. Prior to 1923, call letters beginning with "W" were generally assigned to stations east of an irregular line forming the western borders of states from North Dakota south to Texas, with calls beginning with "K" going to stations in states west of that line. In 1923, the dividing line was shifted to the Mississippi River.