The portion of United States highway 75 from the northern border of Coffey county, then south on United States highway 75 to the northern border of Woodson county is hereby designated as the Floyd H. Robinson memorial highway Vietnam MIA. The secretary of transportation shall place signs along the highway right-of-way at proper intervals to indicate that the highway is the Floyd H. Robinson memorial highway Vietnam MIA, except that such signs shall not be placed until the secretary has received sufficient moneys from gifts and donations to reimburse the secretary for the cost of placing such signs and an additional 50% of the initial cost to defray future maintenance or replacement costs of such signs. The secretary of transportation may accept and administer gifts and donations to aid in obtaining and installing suitable signs.