Well then, when did this exclusive prohibition of refrigerator cars bearing product names relax?
I am thinking of Manufacturer's Railway Service Ralston-Purina checkerboard insulated/ventilated cars, Swift and Armour meat refrigerators with their names on the car sides?
These were running in the 1940's and '50's, carrying the shippers and/or product names.

Ed - 

The ruling still allowed (allows) an exception for these.  Companies can still advertise, but there are a few restrictions.  One is they can only advertise their company name, not any specific product(s).  That is why you have Swift cars, but they just include the corporate name/logo, and not any specific product (e.g. Hams, Bacon).  Also, the cars have to be in captive service for the shipper that leases (or owns them) - resulting in them having to be returned as empties.

These rules are why today we see the Tropicana cars.  They only advertise the company, and are used only by Tropicana
--
Bill Parks
Cumming, GA
Modelling the Seaboard Airline in Central Florida