marker

noun
  1. An object used to indicate a position, place, or route. noun
    The hikers used a stone as a marker to find their way back.
    The race track was lined with cones serving as markers.
  2. A felt-tip pen with a broad tip, used for writing or drawing. noun
    She used a red marker to highlight important points in her notes.
    The artist created a vibrant poster using various colored markers.
  3. A sign or indication of a particular quality or feature. noun
    High blood pressure can be a marker of cardiovascular disease.
    The presence of certain proteins can serve as markers for cancer.
  4. A person or thing that marks. noun
    The teacher acted as a marker for the students' exams.
    In the game, one player is designated as the marker to keep score.