What's the sideways N after the end of the road number on this M&StL boxcar?


 

Hi,

Researching M&StL boxcars, I came across this photo:
http://www.rr-fallenflags.org/misc-m/mstl5038f10.jpg

There is what looks like a sideways N after the road number. Anyone seen anything like it before? What does it mean?

Apologies if this car is too modern here.

Thanks,

Colin

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