Except as otherwise provided in this section, each bus on a motor carrier's roster shall display the motor carrier's legal name or assumed name as listed on its application for authority or official request for name change as submitted to the department and primary telephone number on both sides of the bus in a color that is in sharp contrast to the background color and in a size that is visible from a distance of at least 50 feet. The display required under this section shall meet the vehicle identification requirements of 49 CFR parts 390 to 399. A school bus is not required to display a primary telephone number.