 They were usually painted yellow and often decorated with retro-reflective glass beads or "cats eyes".The name has its origins from the Northern Beaches area of Sydney and was derived from the early days of motoring when policemen would be deployed at busy street corners to direct traffic, before traffic signals became widespread.Silent cops were placed in the middle of street intersections at cross roads, and turning drivers were expected to drive around one, keeping it to the right of the vehicle when turning right or left.