Mass. Gen. Laws ch. 160, § 142

Every county, city and town shall, except as hereinafter provided, and the department of highways shall, unless in any case it deems it unnecessary or impracticable so to do, place and maintain warning signs on every public way subject to its jurisdiction where the way crosses the tracks of a railroad at grade. Said warning signs shall be placed in a conspicuous location beside the public way on each side of the crossing at a distance of not less than two hundred and fifty feet from the nearest rail of the crossing and shall conform in design with the official standards of the department of highways.