Source : Webster's Revised Unabridged Dictionary (1913)

Signboard \Sign"board`\, n.
   A board, placed on or before a shop, office, etc., on which
   ssome notice is given, as the name of a firm, of a business,
   or the like.

Source : WordNet®

signboard
     n : structure displaying a board on which advertisements can be
         posted; "the highway was lined with signboards" [syn: {sign}]