Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 160, § 140

Every railroad corporation shall cause boards, supported by posts or otherwise at such height as to be easily seen by travelers, and not obstructing travel, containing on each side in capital letters at least nine inches long the following inscription,--RAILROAD CROSSING--LOOK OUT FOR THE ENGINE,--to be placed and constantly maintained across each public way where it is crossed by the railroad at the same level; or the corporation may substitute therefor warning boards on each side of the crossing, of such form, size and description as the department approves.