American Bar Association Model Rules of Professional Conduct - Rule 7.4. Communication of Fields of Practice and Specialization
(a) A lawyer may communicate the fact that the lawyer does or does not practice in particular fields of law.
(b) A lawyer admitted to engage in patent practice before the United States Patent and Trademark Office may use the designation "Patent Attorney" or a substantially similar designation.
(c) A lawyer engaged in Admiralty practice may use the designation "Admiralty," "Proctor in Admiralty" or a substantially similar designation.
(d) A lawyer shall not state or imply that a lawyer is certified as a specialist in a particular field of law, unless:
(1) the lawyer has been certified as a specialist by an organization that has been approved by an appropriate state authority or that has been accredited by the American Bar Association; and
(2) the name of the certifying organization is clearly identified in the communication.