CA Pub Util Code Section 1038.5

A passenger stage corporation shall not operate any motor vehicle on a public highway unless there is displayed on the vehicle a distinctive identifying symbol in the form prescribed by the commission, showing the classification to which the vehicle belongs. The identifying symbol shall not be displayed until a certificate of public convenience and necessity has been issued under this chapter for the operation. The identifying symbol displayed by a passenger stage corporation subject to the Interstate Commerce Commission shall serve in lieu of the display requirements of this section.