Mass. Gen. Laws ch. 140 § 137B
Every holder of a kennel license, on delivering an unlicensed dog to a purchaser or to any other person, shall attach to such dog a collar or harness which shall carry a tag marked with the name and address of such kennel licensee, and a number, which number shall be properly recorded on the records of such licensee, and shall also furnish to the person to whom the dog is delivered a certificate bearing the same number and a description of the dog. Such certificate shall bear the date of purchase, exchange or gift and, with the tag, shall, for a period of two weeks following such date, be a legal substitute for a license. The purchaser or other recipient of a dog shall, within two weeks of the purchase or receipt of such dog, either return the same to the licensee from whom it was received, together with the collar or harness, tag and certificate, or return to such licensee said tag, and a certificate signed by the clerk of the town or city where the dog is to be kept and certifying that the dog has been licensed in the name of such purchaser or recipient or of some other person. If any such purchaser or recipient fails to comply with the preceding sentence, such licensee shall notify the clerk of the town or city in which he is licensed of the purchase, exchange or gift of such dog and shall furnish to such clerk the date thereof, and the name and address of the purchaser or recipient.
Mass. Gen. Laws ch. 140, § 137B