Source : Webster's Revised Unabridged Dictionary (1913)

Marker \Mark"er\, n.
   One who or that which marks. Specifically:
   (a) One who keeps account of a game played, as of billiards.
   (b) A counter used in card playing and other games.
   (c) (Mil.) The soldier who forms the pilot of a wheeling
       column, or marks the direction of an alignment.
   (d) An attachment to a sewing machine for marking a line on
       the fabric by creasing it.

Source : WordNet®

marker
     n 1: some conspicuous object used to distinguish or mark
          something; "the buoys were markers for the channel"
     2: a distinguishing symbol; "the owner's mark was on all the
        sheep" [syn: {marking}, {mark}]
     3: a writing implement for making a mark