Older interstate sign with "NORTH CAROLINA". These are very rare on highways today. (Photo by Joe Koehler).
Current style North Carolina state marker. The signs have always been diamond shaped. (Photo from Joe Koehler)
Older sign from the 1950's to the early 70's. Signs from this and all previous eras are cutout diamonds with the fancy 'NC'. A quick side note, this 'NC' insignia first appeared on NC license plates expiring June 1917. (Photo from Mike Summa)
Image scanned from 1962 North Carolina Official Map (black and white edition) showing a NC route marker on a gantry sign (map from my collection)