I think the companies providing railway signalling systems, like Thales, Alstom, Hitachi, Siemens, Westinghouse, would be most likely to supply this sort of sys

I think the companies providing railway signalling systems, like Thales, Alstom, Hitachi, Siemens, Westinghouse, would be most likely to supply this sort of system — or more likely, supply the system behind it but outsource the displays. Here's the company that manufactured the ones for National Rail: https://trueform.com/products/next-train-indicator-nti/ https://trueform.com/products/next-train-indicator-nti/