In this ASP.NET AJAX Chart demo, you can see how to add Notes for the Min and Max values of LineSeries.
To do that you need to set the Series -> DataNoteTextField to a valid field of the chart series. Within the NotesApperance inner tag you
can specify the Note's Icon, Line and Label apperance.
Sample declaration:
<NotesAppearance Position="Bottom">
<Icon Type="Circle" Size="8" BackgroundColor="Transparent" Visible="true">
<Border Width="1" Color="Black" />
</Icon>
<Label Position="Outside" DataFormatString="{0} titles">
<Border DashType="Solid" Color="Black" Width="1" />
<TextStyle Bold="false" Italic="false" FontSize="12" />
</Label>
<Line DashType="Solid" Length="10" Width="1" Color="Black" />
</NotesAppearance>