RadChart supported point mark visual indicators for chart series like Line, Area, Spline, etc. from version one, however, customization of these indicators was hard and certainly not for the faint-hearted. With the latest version of the control released this week (Q1 2009 SP1) we introduced two major improvements that significantly simplify the interaction with the point mark indicators.
Option 1: Customizing the appearance of the point marks through the PointMark API and predefined point mark shapes
RadChart supports 8 predefined shapes that you can use for the point marks (members of the Telerik.Windows.Controls.Charting.MarkerShape enumeration):
Here is a sample code snippet that demonstrates customizing the point mark to use Diamond shape:
And in order to instruct the chart to utilize this template instead of the default one you need to set the SeriesDefinition.PointMarkItemStyle property like this (note that setting fill / stroke through the API would work in this scenario as well):