The chief of police, subject to any directions which the city commission may give by motion or resolution, is hereby authorized to determine those intersections at which drivers of vehicles shall not make a right, left or U-turn, and shall have placed proper signs at such intersections. The making of such turns may be prohibited between certain hours of any day and permitted at other hours; in which event the same shall be plainly indicated on the signs, or they may be removed when such turns are permitted. (2001 Code § 70.060)