There shall be installed, on the exterior of the ends of each debris box, four reflective-type warning devices, each having a red reflecting area of at least three inches in diameter. The devices shall be so placed that one device shall be located near each edge that abuts the side of the box and so that they shall be no less than twenty-four inches or more than forty-eight inches from ground level. (Ord. 162 NS, 1970; prior code § 17A-7.)