In case anyone cares about North American practices; the small lights on the front of the boiler, or on the front of a cab of a Diesel electric unit; they are known as "Classification lights", NOT "Marker lights".
Class lights indicate, when white, that the train is an Extra Train, not shown on the timetable. If showing Green, it indicates that one or more sections of a timetabled train are following. Lights would be shown by night, and flags by day. "Marker Lights" were used on the caboose, to indicate the end of train. Usually RED to the rear, and green to the front and sides. Marker lights usually had 4 lenses.