Which feature is added to a California issued ID to indicate the holder is under 21 years of age?

In California, the feature that indicates a holder is under 21 years of age is the vertical format of the ID. This design choice serves an essential purpose in simplifying the identification process for businesses and law enforcement. The vertical ID is easily recognizable as belonging to a younger individual, which is particularly significant in age-restricted contexts such as alcohol sales. Having a distinct visual cue helps to promote responsible alcohol consumption and enhances compliance with legal age regulations.

The other suggested features do not specifically convey age in this manner. For example, while plastic coating adds durability and a magnetic stripe can provide additional electronic information, neither serves to indicate the age of the ID holder. Therefore, the vertical format is a clear and effective way to identify someone under the legal drinking age.