North Carolina began automobile registration in 1909 and state-issued plates in 1913.  Because the 1913 plates were only issued for three months, and only to newly-registered vehicles, they are incredibly rare today.  Mysterious small boxed numbers appearing in the center of many 1931-36 plates are now known to represent horsepower ratings (1931) and weight classes (1933-36).  The earliest of the three currently valid base plates began issue in 1982.