noun (n)

• structure displaying a board on which advertisements can be posted(noun.artifact)

  Example:
  The highway was lined with signboards.
  

  Synonym:
  sign
  

  source: wordnet30
• 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.(noun)

  source: webster1913