Not to single Bill S. out for abuse, but I've noticed that some of
the boxcars illustrated at the Branchline web site have their AAR
classification stenciled on the side and some don't.
Was it mandatory for a railroad to stencil the AAR classification
of a car (XM, XML, XAP, etc.) on the side of the car, and if so,
when did the AAR make this a rule?