I found the content. For the BAR cars, the text is:
THIS CAR ASSIGNED TO
SPECIAL SERVICE ON
BANGOR & AROOSTOOK
RAILROAD
RETURN PROPERLY VIA
SERVICE ROUTE
I do have documentation for the NH version. The text on the NH scheme is:
WHEN EMPTY RETURN
NEW HAVEN R.R.
VIA SERVICE ROUTE
I believe BAR went to a similar less-wordy note on the sans-serif schemes of the late 1950s/early 1960s.
Thanks for your help, much appreciated.
bb