The 1954 (dated 1955) issue was the first Ontario licence plate that complied with these standards.

In 1956, Canada, the United States, and Mexico came to an agreement with the American Association of Motor Vehicle Administrators, the Automobile Manufacturers Association and the National Safety Council that standardized the size for licence plates for vehicles (except those for motorcycles) at 6 inches (15 cm) in height by 12 inches (30 cm) in width, with standardized mounting holes. Toronto politician and Orange Order leader Leslie Saunders led protests against a proposal to remove the crown in 1948, a decision the government overturned. Exceptions include the 1951 plates, and farm series plates issued in the 1980s and 1990s. The symbol of a crown representing the Crown of Canada has appeared on almost all Ontario licence plates since 1937, when it was first used to commemorate the coronation of King George VI and Queen Elizabeth.

12.2 Illegality of licence plate covers.

2.3 Serial numbers reserved for government officials.

Colt 1911a1 serial number lookup