I think JPL has an example.

If you look real close into the lunette in the example in the catalog you can see some graphics showing thru on the reverse but I cant make out the three letters.

The only reason why I think it's real (part of an actual series) is because every other plaque on the page is real.

This series looks nothing like the picture (B&W) of another series that was shot in Atlantic City. I think it was Victor Lownes holding them at the time.