(1) All motor vehicles, other than those exempt under subsection (2) of this section, must display a permanent marking identifying the name or number, or both, on each side of the power units. For a motor vehicle that is a common or contract carrier under permit by the commission as described in subsection (3)(a) of this section, a private carrier under subsection (4) of this section, or a leased carrier as described in subsection (5) of this section, any required identification that is added, modified, or renewed after September 1, 1991, must be displayed on the driver and passenger doors of the power unit. The identification must be in a clearly legible style with letters no less than three inches high and in a color contrasting with the surrounding body panel.

(2) This section does not apply to (a) vehicles exempt under RCW 81.80.040, and (b) vehicles operated by private carriers that singly or in combination are less than thirty-six thousand pounds gross vehicle weight.

(3) If the motor vehicle is operated as (a) a common or contract carrier under a permit by the commission, the identification must contain the name of the permittee, or business name, and the permit number, or (b) a common or contract carrier holding both intrastate and interstate authority, the identification may be either the commission permit number or the federal vehicle marking requirement established by the United States department of transportation for interstate motor carriers.

(4) If the motor vehicle is a private carrier, the identification must contain the name and address of either the business operating the vehicle or the registered owner.

(5) If the motor vehicle is operated under lease, the vehicle must display either permanent markings or placards on the driver and passenger doors of the power unit. A motor vehicle under lease (a) that is operated as a common or contract carrier under permit by the commission must display identification as provided in subsection (3)(a) of this section, and (b) that is operated as a private carrier must display identification as provided in subsection (4) of this section.