Good points all but there was a polarized version, I have one. Made by "Major" ca. 1930, it has a groove milled in one side that would fit only one way in a specially adapted receptacle in the DS Center floor pocket and was used for the orchestra stand lights when they were in the pit or for the conductor's stand light when on stage. Our stage plugs were retired with our renovation in 1988 but they had been in service in floor and wall pockets since 1930. We still had about 25 in service until then, all adapted to use 2-pin twist plugs.
If I have time I will try this weekend to get a photo to show the "polarized" plug.
Incidentally, I still smile when I remember slipping and grabbing the copper conductors when plugging into a hot circuit. (I told her not to turn on the knife switch until I said it was okay......)