U. S. Navy consular flag, flown in the bow of boats (although not ships) when a consular representative is on board.  This flag has a history dating back to 1777; it was originally just the circle of stars but the "C" was added in 1903.  The State Department uses other versions of this flag in consular offices and other places.  For more information, see here, and Navy document NTP 13(B), section 1001.

The Navy specifications only give the dimensions of the flag, not the exact placement and size of the stars and "C", so I tried to make it look like the provided graphic.
Own work
Carl Lindberg