California Code, Public Utilities Code - PUC § 5386

(a) Every charter-party carrier of passengers, including a charter-party carrier that operates a limousine, shall include the number of its permit or certificate in every written or oral advertisement of the services it offers.

(b) For the purposes of this subdivision, “advertisement” includes, but is not limited to, the issuance of any card, sign, or device to any person, the causing, permitting, or allowing the placement of any sign or marking on or in any building or structure, or in any media form, including newspaper, magazine, radiowave, satellite signal, or any electronic transmission, or in any directory soliciting charter-party transportation services subject to this chapter.