noun (n)

• some conspicuous object used to distinguish or mark something(noun.artifact)

  Example:
  The buoys were markers for the channel.
  

  source: wordnet30
• a distinguishing symbol(noun.communication)

  Synonym:
  mark, marking
  

  source: wordnet30
• a writing implement for making a mark(noun.artifact)

  source: wordnet30
• One who or that which marks.(noun)

  source: webster1913