marker

Noun

WordNet 3.0

Noun (3)

some conspicuous object used to distinguish or mark something“the buoys were markers for the channel”
a distinguishing symbol“the owner's mark was on all the sheep”Synonyms: marking mark
a writing implement for making a mark

Webster's Dictionary (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]