Every school bus and private carrier bus, in addition to any other equipment or distinctive markings required by this chapter, shall bear upon the front and rear thereof, above the windows thereof, plainly visible signs containing only the words "school bus" on a school bus and only the words "private carrier bus" on a private carrier bus in letters not less than eight inches in height, and in addition shall be equipped with visual signals meeting the requirements of RCW 46.37.190
. School districts may affix signs designed according to RCW 46.61.380
informing motorists of the monetary penalty for failure to stop for a school bus when the visual signals are activated.
However, a private carrier bus that regularly transports children to and from a private school or in connection with school activities may display the words "school bus" in a manner provided in this section and need not comply with the requirements set forth in the most recent edition of "Specifications for School Buses" published by the superintendent of public instruction.