Article here.
In California, the standards following the rule on advertising say that it's presumptively misleading to have any commuication that, "states or implies that a member or law firm is 'of counsel' to another lawyer or a law firm unless the former has a relationship with the latter (other than as a partner or associate, or officer or shareholder pursuant to Business and professions Code sections 6160-6172) which is close, personal, continuous, and regular."