You can find Off Indicators at multiple stations on Southeastern High Speed but sadly they are not functional. I would not mind this if they weren't placed in the game but since they are they should be functional. Off Indicator: The Off Indicator is used by the train/platform staff to make sure the platform signal shows a proceed aspect. Usually trains are not allowed to close the doors until the according signal shows a proceed aspect. Skip to 6:08! Similar indicators are used in Germany.
The Dutch Railways have something similar Top to bottom: Departure light 'V' indicating it's a departure light 'vertreklicht' Blue shield indicatting stopping positions at platforms. These can have numbers in them, to signify the amount of cars for which the position is accurate. They should add those when a Dutch route like my proposal gets added. They work exactly like the ones you described
Many countries have such indicators. In major railway stations in Germany, there are also additional indicators for the platform staff, e.g. indicating that a train is arriving at the station. In this German kids TV series, you can see these indicators in use at Köln HBF (filmed in 2002).
