Wash. Rev. Code § 47.36.310
The department is authorized to erect and maintain motorist information sign panels within the right-of-way of the interstate highway system to give the traveling public specific information as to gas, food, lodging, camping, or tourist-oriented business available on a crossroad at or near an interchange. Motorist information sign panels shall include the words "GAS," "FOOD," "LODGING," "CAMPING," or "TOURIST ACTIVITIES" and the letters "RV" next to a gas, food, lodging, camping, or tourist activity sign if the business or destination accommodates recreational vehicles, and directional information. Directional information may contain one or more individual business signs maintained on the panel. The "RV" logo for businesses or destinations that accommodate recreational vehicles shall be placed in the lower right corner of the gas, food, lodging, camping, or tourist activity sign and shall be in the form of a small yellow circle with the letters "RV" in black. In managing the number of individual business signs to be displayed, the department must ensure the use of available space on a panel is maximized. Motorist information sign panels are authorized within the corporate limits of cities and towns and areas zoned for commercial or industrial uses at locations where there is adequate distance between interchanges to ensure compliance with the Manual on Uniform Traffic Control Devices. The erection and maintenance of motorist information sign panels shall also conform to the Manual on Uniform Traffic Control Devices and rules adopted by the state department of transportation. A motorist service or tourist-oriented business located within one mile of an interstate highway shall not be permitted to display its name, brand, or trademark on a motorist information sign panel unless its owner has first entered into an agreement with the department limiting the height of its on-premise [on-premises] signs at the site of its service installation to not more than fifteen feet higher than the roof of its main building measured to the bottom of the on-premise [on-premises] sign. The restriction for on-premise [on-premises] signs does not apply if the sign is not visible from the highway. The department may, on a case-by-case basis, waive the height restriction when an on-premise [on-premises] sign is visible from the rural interstate system. The department shall charge sufficient fees for the display of individual business signs to recover the costs of their installation and maintenance, and shall charge sufficient fees to recover costs for the erection and maintenance of the motorist information sign panels.
RCW 47.36.310