From Consumer Wiki
Meters that monitor mileage for calculation of fees for taxicabs or buses should exhibit a sticker emblem showing inspection by the California Department of Food and Agriculture, Division of Measurement Standards.
Regulations are enforced by inspectors in individual counties throughout California. Random inspections are the usual method for accomplishing compliance with state regulations. Complaints about meters can be reported to the consumer's County Weights and Measures office.
Weights and Measures (County)