Whenever this Traffic Code or any other ordinance of this Municipality designates and describes a through street, it shall be the duty of the Chief of Police to place and maintain a stop sign, or, on the basis of an engineering and traffic investigation at any intersection, a yield sign, on each street intersecting such through street, unless traffic at any such intersection is controlled at all times by traffic-control signals; provided, that at the intersection of two such through streets or at the intersection of a through street and a heavy traffic street not designated as a through street, stop signs shall be erected at the approaches of either of such streets as may be determined by the Chief of Police upon the basis of an engineering and traffic study.