United States highway 77 from its south junction with United States highway 77 business, thence north to the north junction with United States highway 77 business, is hereby designated as the Walnut Valley greenway. The secretary of transportation shall place highway signs along the highway right-of-way at proper intervals to indicate that the highway is the Walnut Valley greenway, 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. The secretary of transportation may accept and administer gifts and donations to pay for the cost of such highway signs bearing the proper approved inscription.