The department may install adopt-a-highway signs, with the following restrictions:
(1) Signs shall be designed by the department and may only include the words "adopt-a-highway litter control facility" or "adopt-a-highway litter control next XX miles" and the name of the litter control area sponsor. The sponsor's name shall not be displayed more predominantly than the remainder of the sign message. Trademarks or business logos may be displayed;
(2) Signs may be placed along interstate, primary, and scenic system highways;
(3) Signs may be erected at other state-owned transportation facilities in accordance with RCW 47.40.100
(4) For each litter control area designated by the department, one sign may be placed visible to traffic approaching from each direction;
(5) Signs shall be located so as not to detract from official traffic control signs installed pursuant to the manual on uniform traffic control devices adopted by the department;
(6) Signs shall be located so as not to restrict sight distance on approaches to intersections or interchanges;
(7) The department may charge reasonable fees to defray the cost of manufacture, installation, and maintenance of adopt-a-highway signs.