This is the "diver down" flag:. . . . . . .

It floats on the surface and is towed by the diver. Boats are not supposed to come closer than 150 feet of the flag. That is a safety precaution for when the diver surfaces.

Here I am towing the flag. It is attached to the line from the handle that is slid over my arm. The handle could also be clipped to the diving BCD jacket.

It is important to not drop the line.