Mass. Gen. Laws ch. 94 § 323A
No person shall distribute, sell or offer for sale any plastic bottle or rigid plastic container, or any product in such a bottle or container, unless such product bottle or container is labeled with a code indicating the plastic resin used to produce the bottle or container. Plastic bottles or rigid plastic containers with labels and basecups of a different material shall be coded by their basic material. Such code shall consist of a number placed within a triangle of arrows and letters placed below the triangle of arrows. The triangle shall be equilateral, formed by three arrows with the apex of each point of the triangle at the midpoint of each arrow, rounded with a short radius. The arrowhead of each arrow shall be at the midpoint of each side of the triangle with a short gap separating the pointer from the base of the adjacent arrow. The triangle, formed by the three arrows curved at their midpoints shall depict a clockwise path around the code number. The numbers and letters used shall be as follows:
Mass. Gen. Laws ch. 94, § 323A