Bill wrote:

“One of the comments says, The horizontal white stripe on the door indicates that the car has automobile-loading racks".  Was this "standard" across all railroads, or just for certain roads?  I ask, because not all of the cars shown have the stripe (for instance SP 64210).”

The 3” wide white stripe was the original standard marking for cars equipped with auto loading devices as adopted by the ARA in 1933.  The stripe was to be applied to the right door, though (early on) many roads decorated both doors.  

The right door on SP 64210 is obscured by the automobile, but the stripe is (more than likely) there.

Guy Wilber

Reno, Nevada