It shall be unlawful for any person other than an officer of the police department or members of the fire department, a person deputized or authorized by the chief of police or a person otherwise 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 engineer.  (Ord. 486 § 4 (part), 1992:  prior code § 13-3.1)