Source : Webster's Revised Unabridged Dictionary (1913)

Fanion \Fan"ion\, n. [See {Fanon}.]
   1. (Mil.) A small flag sometimes carried at the head of the
      baggage of a brigade. [Obs.]

   2. A small flag for marking the stations in surveying.

Source : WordNet®

fanion
     n : a small flag used by surveyors or soldiers to mark a
         position