Eric Hansmann wrote:
N&W cars have a similar white square. Andrew Dow notes in his N&W hopper book that these painted squares denote the area for placards and route cards. Car men didn’t always oblige when racking up the documents.
Actually, if you look at photos, carmen RARELY put the route cards where indicated. Likely an expression of independence. Most railroads made those paint squares black.
Tony Thompson Editor, Signature Press, Berkeley, CA
Publishers of books on railroad history