RCW 46.37.187: Green light, sign or plate—Identification card required.

Any individual displaying a green light as authorized in RCW 46.37.185, or a sign or plate as authorized in RCW 46.37.186, shall also carry attached to a convenient location on the private vehicle to which the green light or sign or plate is attached, an identification card showing the name of the owner of said vehicle, the organization to which he or she belongs and bearing the signature of the chief of the service involved.