Are you asking about "Classification lights", or "Marker Lights" ?
There is a difference.
The small lights carried on the front of older locomotives were "Classification lights", or "Class lights"
Marker lamps were on the end of a "Train" ....common statement was....."Markers bring up the rear.......
Then of course there is a difference in what constitutes a "Train"
Many people call anything that is on a set of rails, a train....this is not always correct.