Mass. Gen. Laws ch. 147 § 29
No licensee or employee or agent of a licensee shall use a badge of any kind for identification purposes except a guard or watchman in uniform who shall wear any such badge on the left breast of his uniform. Such badge shall not contain the word "Police" or any part of the seal of the Commonwealth of Massachusetts or of any political subdivision thereof. A licensee or his employee or agent shall carry only such weapons and equipment as are authorized by the colonel of the state police; provided, however, that if said licensee, employee or agent, is authorized to carry a firearm, as defined in section one hundred and twenty-one of chapter one hundred and forty, said firearm shall be loaded while in the performance of his duties. A licensee, or his employee or agent, while in the performance of his duties, shall not carry an imitation firearm as defined in said section one hundred and twenty-one of said chapter one hundred and forty. A licensee or his employee or agent may use as identification a card, approved as to form by the colonel of the state police, which shall bear the signature of the licensee and, if such card is used as identification by an employee or agent, the signature of such employee or agent.
No motor vehicle used in the business of a licensee shall have displayed therein or thereon the words "police" or "emergency", and no such motor vehicle shall be deemed to be a special purpose motor vehicle assigned to emergency disaster services under the provisions of section seven I of chapter ninety.
Whoever violates any provision of this section shall be punished by a fine of not more than fifty dollars.
Mass. Gen. Laws ch. 147, § 29