California Code, Penal Code - PEN § 602.7

Every person who enters or remains on any property, facility, or vehicle owned by the San Francisco Bay Area Rapid Transit District or the Southern California Rapid Transit District, and sells or peddles any goods, merchandise, property, or services of any kind whatsoever on the property, facilities, or vehicles, without the express written consent of the governing board of the San Francisco Bay Area Rapid Transit District or the governing board of the Southern California Rapid Transit District, or its duly authorized representatives, is guilty of an infraction.

Nothing in this section affects the power of a county, city, transit district, or city and county to regulate the sale or peddling of goods, merchandise, property, or services.