Neither the company nor the reporting mark is listed in my January 1939 ORER (nor in others of mine, from 1926 to 1960), but Northern Indiana dot-dot-dot does show up after the end of the world (1960) in my 1965 ORER, apparently with several hundred coal gons.
I have found cars with reporting marks that don't show up in the ORER before. I suppose that inclusion in the ORER is/was voluntary and perhaps even involved giving money to the publisher. Maybe perhaps.
I sure do wonder when the ad photo was taken. And where. 'Cause the car existed, even if the ORER says it didn't.
And there's a bit of curiosity about why a utility company would have a car like this (or 8 of them???). Was it load in or load out?
Thank you all for moving this project of mine forward. With the ad photo, I can pretty much figure out the "good-enough-for-me" lettering (though I guess the color might be either white or yellow--there's a puzzle) and the tank color (with the lack of graphic enthusiasm exhibited by the owner, I'm going with black).
Also looming (perhaps) is the possibility that an NIPX tank car would never roll over the rails in my modeling locale. Tony's suggestion of a wine tank car might lead me down the (possibly horrendous) freelance route. The car's next owner might be happy that paint strips easily off of a metal model.