The maximum permitted speed is shown using signs with either yellow numbers or reflectorised circular signs with a red border and black numbers. At various places on the track, such as for points or curves, permanent speed restrictions (PSR) are imposed. If the approach speed is 60 mph or more and the speed restriction represents one third or more of the approach speed, a warning indicator is displayed to give the driver time to slow down the train. Warning indicators are reflectorised triangular signs with a yellow border and black numbers, and may also contain an arrow if pointing to a diverging line. They may also display two numbers where differential speeds apply: the bottom number refers to passenger trains, light locomotives and postal vehicles; the top number refers to all other trains. The end of the PSR is denoted by a termination indicator.