To create a marker for your label, complete the following:
c1Chart1.ChartArea.AxisX.AnnoMethod = C1.Win.C1Chart.AnnotationMethodEnum.Mixed
Dim vl As ValueLabel = c1Chart1.ChartArea.AxisX.ValueLabels.AddNewLabel()
vl.Appearance = ValueLabelAppearanceEnum.TriangleMarker
vl.MarkerSize = 50
vl.Color = Color.Transparent
vl.NumericValue = 2
•C#
C1Chart1.ChartArea.AxisX.AnnoMethod = C1.Win.C1Chart.AnnotationMethodEnum.Mixed
Dim markerX As C1.Win.C1Chart.ValueLabel = C1Chart1.ChartArea.AxisX.ValueLabels.AddNewLabel()
markerX.NumericValue = 3
markerX.Moveable = True
markerX.MarkerSize = 15
markerX.GridLine = True
markerX.Color = Color.Blue
markerX.Appearance = C1.Win.C1Chart.ValueLabelAppearanceEnum.ArrowMarker