That portion of interstate highway 135 from the northern boundary of McPherson county, then south on interstate highway 135 to the southern boundary of Harvey county is hereby designated the Vietnam war veterans memorial highway. The secretary of transportation shall place signs at each entrance onto interstate highway 135 in McPherson and Harvey counties indicating that the highway is the Vietnam war veterans memorial highway, 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 costs to defray future maintenance and replacement cost of such signs. The secretary of transportation may accept and administer gifts and donations to aid in obtaining and installing suitable signs.