In 1956, the United States, Canada, 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 license 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.

Any officially manufactured California license plates which were produced prior to 1963 can be used on a currently registered vehicle or trailer of a corresponding model year.

[33] As of January 2014[update], in very rare cases, California has extended custom license plates to allow more than seven digits, but not to exceed nine characters.

[citation needed] In August 2016, California extended the year-of-manufacture license plate program to include vehicles through the 1980 model year.

[36][37] Prior to 2019, California was the last U.S. state to not require the display of any form of temporary license plate on new vehicles.

[25] The dealer was then only required to attach the DMV report-of-sale form to the inside of the car windshield in the lower right corner (from the driver's perspective).

[40] Before 2019, it was common for a newly purchased vehicle to be driven around for a month (or more) with nothing but a dealer's advertisement or logo on paper plate inserts in the mounting brackets where the owner was supposed to promptly install front and rear license plates when they arrived in the mail from the DMV.

California's lack of a temporary license plate requirement was mocked as the "Steve Jobs loophole," due to the Apple founder's habit of continuously signing a series of six-month leases of Mercedes-Benz SL55 AMGs on a rolling basis for the specific purpose of avoiding the state requirement of having to install permanent license plates on his cars.

[41] The DMV report-of-sale forms were printed in regular type not intended to be read at a distance, meaning that it was legible only to persons leaning closely over the windshield when the car was standing still.

This made the new vehicle untraceable through casual visual observation by passerby (especially for the common car models and colors), as well as automated means such as license-plate reading systems, red light cameras, and automatic number plate recognition.

[25] This loophole was also deliberately exploited by criminals, who knew that a car with dealer paper inserts was untraceable and in and of itself would not raise suspicion.

[42] The hit-and-run death of a pedestrian who was struck by an unidentifiable car with dealer paper inserts sparked the enactment of new legislation in 2016 to require temporary license plates in California beginning in 2019.

The series that the temporary license plates use is AB12C34, and it applies to all newly purchased vehicles in the state of California since 2019.