Mass. Gen. Laws ch. 90 § 5A
The adjutant general, in behalf of the military forces of the commonwealth, may make application, in such form and containing such information as the registrar may determine, for a general distinguishing mark, and the registrar shall issue to him a certificate of registration. All motor vehicles under the control of the military forces of the commonwealth shall be regarded as registered under such general distinguishing mark, provided said mark is properly displayed thereon.
Each vehicle registered in accordance with this section shall display the general distinguishing mark and different letters or numbers, or a combination thereof, assigned to it by the adjutant general, which shall be in such form and displayed as the registrar shall approve.
Whoever upon any way of the commonwealth operates a motor vehicle to which marks of distinction, as provided in this section, have been attached without authority, or whoever without authority operates a motor vehicle to which such marks have been legally attached, shall be punished by a fine of not less than twenty-five nor more than fifty dollars.
Mass. Gen. Laws ch. 90, § 5A