My understanding is that all engines in passenger service, or that could be assigned to passenger service would be required to carry train indicator boards. I believe this was a D&RGW policy. The odd thing is that while the narrow gauge engines were so supplied, I don't ever recall seeing a picture of a passenger train with the train number displayed on the boards. Only the engine number. The UP used these for train numbers and "extra" numbers, which would carry the engine number preceeded by an "X".
I don't have a clue why 487 doesn't have boards now, but she didn't have them in the fifties or sixties, either, and didn't come to the C&TS with any.
Mike