'Marker' definitions:

Definition of 'marker'

From: WordNet
noun
Some conspicuous object used to distinguish or mark something; "the buoys were markers for the channel"
noun
A distinguishing symbol; "the owner's mark was on all the sheep" [syn: marker, marking, mark]
noun
A writing implement for making a mark

Definition of 'Marker'

From: GCIDE
  • 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. [1913 Webster]