Mass. Gen. Laws ch. 159, § 92: Badges

Section 92. Special police officers appointed by the colonel of state police under the provisions of section fifty-one of chapter twenty-two C shall, when on duty except as detectives, wear in plain sight a metallic badge, inscribed with the words, ''Railroad Special Police'', ''Street Railway Special Police'', ''Railway Express Special Police'' or ''Steamboat Special Police'', as the case may be, and the name or initials of the corporation or company for which they are appointed; and the presence of any such officer on the cars, vehicles, steamboats or premises of the corporation or company upon whose petition he was appointed, wearing such badge, shall be prima facie evidence that he is lawfully upon duty.