RCW 47.40.060

If any such permit is granted, the department shall enter into an agreement with the person, firm, corporation, association, or organization agreeing that such roadside development or beautification shall be maintained and kept up by the state through the department or by the person, firm, corporation, association, or organization. If any such person, firm, corporation, association, or organization so agreeing fails or neglects to maintain the roadside development or beautification, the department is empowered to do so, and the expense thereof shall be a charge against the person, firm, corporation, association, or organization.