Diver-Down Flags
Divers Flag: A rectangular red flag with a white diagonal stripe can be attached to a watercraft, float, or buoy.
Alfa Flag: A blue-and-white International Code Flag A (or Alfa flag), at least 3.3 feet (one meter) high and visible from all directions, must be displayed on vessels on federally controlled waters. This flag indicates that the vessel is involved in a diving activity.