Unless excepted every motor vehicle owned or controlled by any county shall bear on both sides thereof the following inscription: “For Official Use Only”. Underneath the inscription shall be the name or title of the county and the name of the department, commission, board, bureau, [office], agency, or instrumentality thereof controlling or possessing the motor vehicle; except that every motor vehicle owned or controlled by the board of water supply of the city and county of Honolulu shall bear on both sides thereof the following inscription: “Board of Water Supply – Conserve Water”. This section shall not apply to motor vehicles that are furnished to the mayor of the city and county of Honolulu or to the chairperson and executive officer of the council of any county, or to the chief of police and deputy chief of police of the city and county and counties or manager of the board of water supply of the city and county of Honolulu.