It shall be the duty of the secretary of transportation to cooperate with any person or group of persons so interested in placing markers at proper intervals along any highway right-of-way indicating the points where said Smoky Hill trail runs parallel with or crosses any state highway. Said markers shall be made from the famous stone fence posts prominent in western Kansas, and said markers will be made showing a 30-inch shaft above a cement base and on the side facing any highway a panel is to be smoothed and the legend, B.O.D., 1865 (meaning Butterfield overland dispatch, the official title of the firm establishing this trail) sandblasted on in letters large enough to be easily read by anyone passing by on the highway.