public bool AngleToLine {get; set;}

//These methods must be called within the lambda passed to QueuedTask.Run
var lineStrokeRed = SymbolFactory.Instance.ConstructStroke(ColorFactory.Instance.RedRGB, 4.0);
var markerCircle = SymbolFactory.Instance.ConstructMarker(ColorFactory.Instance.RedRGB, 12, SimpleMarkerStyle.Circle);
markerCircle.MarkerPlacement = new CIMMarkerPlacementOnVertices()
{
  AngleToLine = true,
  PlaceOnEndPoints = true,
  Offset = 0
};
var lineSymbolWithCircles = new CIMLineSymbol()
{
  SymbolLayers = new CIMSymbolLayer[2] { markerCircle, lineStrokeRed }
};

//These methods must be called within the lambda passed to QueuedTask.Run
var markerTriangle = SymbolFactory.Instance.ConstructMarker(ColorFactory.Instance.RedRGB, 12, SimpleMarkerStyle.Triangle);
markerTriangle.Rotation = -90; // or -90
markerTriangle.MarkerPlacement = new CIMMarkerPlacementOnLine() { AngleToLine = true, RelativeTo = PlacementOnLineRelativeTo.LineEnd };

var lineSymbolWithArrow = new CIMLineSymbol()
{
  SymbolLayers = new CIMSymbolLayer[2] { markerTriangle,
              SymbolFactory.Instance.ConstructStroke(ColorFactory.Instance.RedRGB, 2)
          }
};