Wash. Rev. Code § 18.200.030
No person may represent himself or herself as a licensed orthotist or prosthetist, use a title or description of services, or engage in the practice of orthotics or prosthetics without applying for licensure, meeting the required qualifications, and being licensed by the department of health, unless otherwise exempted by this chapter.
A person not licensed with the secretary must not represent himself or herself as being so licensed and may not use in connection with his or her name the words or letters "L.O.," "L.P.," or "L.P.O.," or other letters, words, signs, numbers, or insignia indicating or implying that he or she is either a licensed orthotist or a licensed prosthetist, or both. No person may practice orthotics or prosthetics without first having a valid license. The license must be posted in a conspicuous location at the person's worksite.
RCW 18.200.030