Many years ago now, when I was commuting into Bristol from Nailsea, a Pacer approached the station with red lights displayed to the front. A semi-uniformed member of railway staff, who I assumed was also catching that train on his own way in to work, discreetly gestured to the train driver that his lights were not right. The driver promptly corrected them, with a nod of acknowledgement to his colleague on the platform as he passed.