This is an interesting little thread!
I think a great case can be made for what Checker and Ludwig-D and others propose. Walberg seemed to have made and supplied the same pedal for many. With the quantity that Frank’s ordered (clout, heck there is a whole book written about Frank’s) on a regular basis, and back then, it could have been a special thing for Frank’s as well as a way to keep track of that models destination during production and packing (I understand Frank’s could be demanding on manufacturers). A good way not to get the orders for this same pedal for other companies mixed.
Kevins, it would be pretty easy for the manufacturer to do as you suggested instead of the retailer; stamp the mold and produce many with raised letters, as to not ship to Gretch, Camco and others.