Rear vehicle maximum-speed plates

The image shows circular plates marked 60, 80 and 100. They are affixed to the rear of specified categories of vehicle and inform following traffic of the maximum speeds that apply to that vehicle, commonly with different values for different road categories. In the official questions, these plates may be fitted to certain buses. They are not the plates used for motorcycles, motor caravans up to 3.5 tonnes or goods vehicles up to 3.5 tonnes.