noun (n)

• a distinctive characteristic or attribute(noun.attribute)

  Synonym:
  earmark, stylemark, trademark
  

  source: wordnet30
• a mark on an article of trade to indicate its origin and authenticity(noun.communication)

  Synonym:
  assay-mark, authentication
  

  source: wordnet30
• The official stamp of the Goldsmiths' Company and other assay offices, in the United Kingdom, on gold and silver articles, attesting their purity. Also used figuratively; -- as, a word or phrase lacks the hall-mark of the best writers.(noun)

  source: webster1913