Greg/Tom,
In the book of US HQ flags noted by Nick, let me note the several lookalikes that could be confused with US Signal Corps signal flgs or vice versa. Conversely, on the last page of the book, the flag of the signal corps is in error -- the "star flag," which was awarded to a signal officer who distinguished himself under fire, was never combined with another flag (and torch). Also you'll note the elongated rectangular center of the white flag, as opposed to a square flag and square centerpiece.