Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 142, § 17

No range boiler, tank, vessel or container, ferrous or non-ferrous, in which water is to be heated or stored under pressure for domestic, culinary or sanitary purposes, in this section and in sections eighteen and nineteen referred to as hot water tanks, shall be sold or offered for sale unless it is plainly marked by the manufacturer, by stamping into the metal of the tank, or on a metal plate permanently attached to the tank, in a conspicuous place, as follows:--

Notwithstanding the requirements of the preliminary paragraph and paragraphs A to D, inclusive, of this section, the markings therein referred to shall not be required, in the case of cast iron hot water fronts, so called, or hot water tanks that are insulated or enclosed in a jacket or casing, to be stamped into the metal thereof or to be stamped on a metal plate permanently attached thereto; provided, that any manufacturer selling such hot water fronts within the commonwealth shall in writing certify to the department of fire services and the board of state examiners of plumbers that every such water front sold by him complies with the pertinent provisions of law; and provided, further, that any manufacturer of hot water tanks that are insulated or enclosed in a jacket or casing which are to be sold within the commonwealth shall certify in writing to the department of fire services and the board of state examiners of plumbers that every such tankless water heater coil or element, or hot water tank manufactured by him complies with the pertinent provisions of law, and shall permanently attach to the largest segment of said jacket or casing, in a conspicuous place, a metal plate which has stamped into the metal thereof the requirements of paragraphs A to D, inclusive.