Washington Revised Code Title 46. Motor Vehicles § 46.55.070. Posting requirements--Exception

(1) No person may impound, tow, or otherwise disturb any unauthorized vehicle standing on nonresidential private property or in a public parking facility for less than twenty-four hours unless a sign is posted near each entrance and on the property in a clearly conspicuous and visible location to all who park on such property that clearly indicates:

(2) The requirements of subsection (1) of this section do not apply to residential property. Any person having charge of such property may have an unauthorized vehicle impounded immediately upon giving written authorization.

(3) The department shall adopt rules relating to the size of the sign required by subsection (1) of this section, its lettering, placement, and the number required.

(4) This section applies to all new signs erected after July 1, 1986. All other signs must meet these requirements by July 1, 1989.