Mass. Gen. Laws ch. 101 § 27
Every person licensed as a hawker or pedler shall endorse his usual signature upon his license. The deputy director shall, at the expense of the licensee, provide a means for displaying such license which must be worn in a visible and conspicuous manner on his outer clothing with the license number, licensee's name and the date of expiration exposed to view. Each licensee shall produce his license for inspection whenever demanded by the deputy director or by a mayor, alderman, selectman, inspector of standards, sealer or deputy sealer of weights and measures, city or town treasurer or clerk, constable, police officer or justice of the peace; and if he fails so to do, or fails to wear his license in a visible and conspicuous manner as heretofore prescribed, he shall be subject to the same penalty as if he had no license.
Mass. Gen. Laws ch. 101, § 27