Mass. Gen. Laws ch. 222 § 5
A person appointed commissioner in a state, territory, district or dependency of the United States shall, within three months after his appointment, take and subscribe an oath before a justice of the peace or other magistrate of the town or county where he resides, or before a clerk of a court of record within the state, territory, district or dependency where he resides, faithfully to perform the duties of his office, and shall cause an official seal to be prepared, upon which shall appear his name, the words "Commissioner for Massachusetts" and the name of the state, territory, district or dependency, and town or county where he resides. A person appointed commissioner in a foreign country shall, before performing any duty of his office, take and subscribe an oath before a judge or clerk of a court of record of the county where he resides or before an ambassador, minister or consul of the United States, accredited to such country, faithfully to perform the duties of his office. In each case, a certificate of the commissioner's oath of office and his signature and an impression of his official seal shall be forthwith transmitted to and filed in the office of the state secretary.
Mass. Gen. Laws ch. 222, § 5