PROFESSIONAL CARD. The customary use of professional cards is permissible. The professional card of a member may with propriety contain only a statement of the member's name (and the names of lawyers associated with him), profession, address, telephone number, and special branches of the profession practiced. The professional card, or the professional listing, may be inserted in reputable law lists and law directories. The listing shall contain only such matter permitted in the professional card, but may include a brief biographical sketch of the lawyer and his associates, and, with their written consent, the names of not more than six representative clients for whom the lawyer and his associates are regularly employed as counsel.