The Collaborative International Dictionary of English v.0.48:

Insignia \In*sig"ni*a\, n. pl. [L. insigne, pl. insignia, fr.
   insignis distinguished by a mark; pref. in- in + signum a
   mark, sign. See Ensign, Sign.]
   [1913 Webster]
   1. Distinguishing marks of authority, office, or honor;
      badges; tokens; decorations; as, the insignia of royalty
      or of an order.
      [1913 Webster]

   2. Typical and characteristic marks or signs, by which
      anything is known or distinguished; as, the insignia of a
      trade.
      [1913 Webster]

WordNet (r) 3.0 (2006):

insignia
    n 1: a badge worn to show official position

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "insignia":
   badge, banner, character, characteristic, decoration, device,
   differentia, earmark, emblem, hallmark, idiosyncrasy, image, index,
   indicant, indicator, keynote, mark, measure, note, peculiarity,
   picture, property, regalia, representation, representative, seal,
   sigil, sign, signal, signature, stamp, sure sign, symptom,
   telltale sign, trait