It is unlawful for any person other than an officer of the Police Department or members of the Fire Department or a person authorized by the Chief of Police or a person authorized by law to direct or attempt to direct traffic by voice, hand or other signal, except that persons may operate, when and as herein provided, any mechanical push-button signal erected by order of the City Traffic Engineer. (Ord. 3262-NS § 2.1, 1952)