A commercial vehicle in California must have a name or trademark displayed on both sides of each vehicle, legible from 50 feet during daylight hours, of the person under whose authority the vehicle or combination is being operated or the name of the lessor or lessee. The relevant California Vehicle (CVC) Sections 27900(a) and 27901 are copied below (with bolding added):
27900. (a) Every motor vehicle or combination of vehicles used to carry the property of others for hire or used to carry passengers for hire, any truck or truck tractor having three or more axles or any truck tractor with a semitrailer, and all commercial motor vehicles, as defined in subdivision (c) of Section 34601, shall have displayed on both sides of each vehicle or on both sides of one of the vehicles in each combination of vehicles the name or trademark of the person under whose authority the vehicle or combination of vehicles is being operated.
27901. The display of the name or trademark shall be in letters in sharp contrast to the background and shall be of such size, shape, and color as to be readily legible during daylight hours from a distance of 50 feet. This section does not prohibit additional displays not inconsistent with this article.
For more information on name or trademark displays, contact the Commercial Vehicle Section of the California Highway Patrol (CHP) at (916) 843-3400.