The Chief of Police shall determine the character of all official traffic-control devices and shall have the exclusive right to establish and maintain all official traffic-control devices in the city, when and as required under this traffic code, and may place and maintain such additional traffic-control devices as he may deem necessary. All traffic-control devices shall be the same general type and all such traffic devices employed to indicate one particular warning or regulation shall be uniform and as far as possible shall be placed uniformly. All signs shall conform to those recommended by the National Conference on Street and Highway Safety.