An SP employee who worked at Gemco (yard near GM Van Nuys) mentioned that freight cars for the plant would occasionally come in with an "unload this side" placard that needed to match the loading dock configuration.  There was an air-operated turntable at the yard that could be used to turn incorrectly-facing freight cars, but it was balky and often not functioning.  The backup solution was to run the cars several miles down the mainline to a wye at Burbank Junction.  If there wasn't time to reverse the car, then the placard would mysteriously disappear and the car would be delivered as-is.

Robert