http://www.mass.gov/legis/laws/mgl/130-38a.htm
Chapter 130: Section 38A. Display of license number and buoy colors
Section 38A.
No person or persons shall take or attempt to take, by diving, lobsters, or edible crabs from the coastal waters, unless he displays his lobster license number upon his air tank, and for each person diving alone or for each group of divers upon the surface of said waters, in the area where the person or persons is taking or attempting to take lobsters and edible crabs, a floating marker shall be displayed with the
license number of each person diving alone or in the case of any group of divers the license number of every person taking or attempting to take lobsters shall be displayed. Said number on a floating marker shall be displayed in the form of a single panel not less than twelve inches in height and width and shall be buoyed in an upright position. The marker shall have a white background with the licensees number, or in the case of a group the licensees numbers, displayed on both sides thereof by black numerals of a size prescribed by regulation of the director.