Section 39C. The collector of a city or town may in writing appoint, with approval of the mayor or the selectmen thereof, an assistant collector who may be an employee in said collector’s department. The assistant collector shall be sworn to the faithful performance of his duties, and a record shall be made of his appointment and oath. The assistant collector shall be a citizen of the United States and shall give bond annually for the faithful performance of his duties in a form approved, and in an amount determined by the commissioner of revenue. Unless a temporary collector is appointed in accordance with law, the assistant collector may, in the absence of the collector, perform his duties and when performing such duties shall have the powers and be subject to the requirements and penalties applicable to him; provided, however, that the assistant collector shall not be authorized to sign for the collector instruments of taking pursuant to section fifty-four of chapter sixty. The person appointed as assistant collector may receive a salary from the city or town for service as such.