PDFWAC 308-61-145
Specifications and posting of signs.
How is the posting of signs on private and public property handled?
(1) Signs must measure at least 15" by 24" and the lettering thereon must be clearly visible to all who park.
(2) Signs for publicly owned or controlled parking facilities need to disclose that unauthorized vehicles will be impounded and must also disclose a phone number for redeeming a vehicle. If a registered tow truck operator is used, the signs must meet the same requirements as in the posting of private nonresidential property.