Mass. Gen. Laws ch. 90B § 13A
Every scuba diver or group of scuba divers while swimming on or under the surface of the waters of the commonwealth shall display for each diver or group of divers as a warning device to boat operators, a diver's flag, so called, constructed of rigidly supported material at least twelve inches by fifteen inches in area of red background with a white diagonal stripe. Such diver's flag shall be displayed on a boat or surface float and shall extend a minimum distance of three feet from the surface of the water. Divers shall remain in an area within one hundred feet of such displayed diver's flag while at or near the surface of the water. A boat operator within sight of a diver's flag shall proceed with caution and within a radius of one hundred feet of such flag shall proceed at a speed not to exceed three miles per hour.
Mass. Gen. Laws ch. 90B, § 13A