Conn. Gen. Stat. § 14-103d: Vehicles using any pressurized gas as fuel. Regulations. Class C misdemeanor.

(a) No motor vehicle which uses any pressurized gas except natural gas or hydrogen as a fuel for its engine may enter or be parked in any area that is under grade level. Any vehicle within the state which carries any pressurized gas as its fuel in a tank attached to the vehicle in any concealed area, including, but not limited to, trunks, compartments or under such vehicle, except a vehicle that is in compliance with all applicable federal codes and standards for light duty passenger use, shall have displayed on its exterior the words “Pressurized Flammable Gas” or a standard abbreviation or symbol as determined by the Office of the State Fire Marshal, in block letters at least two inches high, which letters shall be of contrasting colors and shall be placed as near as possible to the area where the tank is located. No person may dispense any pressurized gas used as a vehicle fuel into any tank in a concealed area of a vehicle unless the vehicle is in compliance with the requirements of this subsection. The Commissioner of Motor Vehicles shall adopt regulations in accordance with the provisions of chapter 54 to carry out the provisions of this section.

(b) Any person who violates any provision of this section or any regulation adopted pursuant to this section shall be guilty of a class C misdemeanor.