The portion of U.S. Highway 63, from the southern-most city limits of a city of the fourth classification with more than one thousand nine hundred eighty but less than two thousand eighty inhabitants south to the exit for State Route Z, all located within a county of the third classification with a township form of government and with more than twenty-three thousand but less than twenty-three thousand one hundred inhabitants, shall be designated the “Trooper Kelly L. Poynter Memorial Highway”. The department of transportation shall, at their discretion, erect and maintain signs commemorating this portion of U.S. Highway 63.