The black around the lettering was used on a number of cars during this period.
I've heard that it signified an air conditioned car, but can't say for certain.
It was later discontinued.
Yep, you got it right.
The lettering was used on heavyweight cars that were retrofitted to AC between
1936 and 1942.
All lightweight cars delivered between 1936 and 1948, including head-end cars,
were delivered with black letter-board panel lettering.
And few AC business cars received the lettering scheme too.
A couple non-AC revenue cars got the lettering just to make it confusing. They
were used as tail-end cars on a couple regional trains.
And a few non-AC private cars including dynamometer car #62 got the treatment
too.
Jeff Pinchbeck
