Hello Sofiane!

Replasing the axis thumb with an icon is possible. Here is how to achieve this:

<ig:XamTimeline>

  <ig:XamTimeline.Axis>

    <ig:NumericTimeAxis>

      <ig:NumericTimeAxis.ThumbStyle>

        <Style TargetType="ig:AxisThumb">

          <Setter Property="Width"

                  Value="32" />

          <Setter Property="Height"

                  Value="32" />

          <Setter Property="Template">

            <Setter.Value>

              <ControlTemplate TargetType="ig:AxisThumb">

                <Image Source="star.png"

                       Width="32"

                       Height="32" />

              </ControlTemplate>

            </Setter.Value>

          </Setter>

        </Style>

      </ig:NumericTimeAxis.ThumbStyle>

    </ig:NumericTimeAxis>

  </ig:XamTimeline.Axis>

</ig:XamTimeline>

You can re-style the axis thumb with: timeline.Axis.ThumbStyle property. Here is a sample with the default style of the axis thumb.

<UserControl

       xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

       xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

       xmlns:ig="http://schemas.infragistics.com/xaml"

       x:Class="SilverlightApplication11.MainPage"

       Width="640" Height="480">

    <UserControl.Resources>

        <SolidColorBrush x:Key="BaseColorBrush" Color="#FF1F3B53"/>

        <LinearGradientBrush x:Key="BaseBorderBrush" EndPoint="0,1" StartPoint="0,0">

            <LinearGradientBrush.GradientStops>

                <GradientStopCollection>

                    <GradientStop Color="#FFa3aeb9" Offset="0"/>

                    <GradientStop Color="#FF8399a9" Offset="0.3700000047683716"/>

                    <GradientStop Color="#FF718597" Offset="0.3709999918937683"/>

                    <GradientStop Color="#FF617584" Offset="1"/>

                </GradientStopCollection>

            </LinearGradientBrush.GradientStops>

        </LinearGradientBrush>

        <LinearGradientBrush x:Key="BaseOverlayBrush" EndPoint="0.5,1" StartPoint="0.5,0">

            <LinearGradientBrush.GradientStops>

                <GradientStopCollection>

                    <GradientStop Color="#FFffffff" Offset="0"/>

                    <GradientStop Color="#f9ffffff" Offset="0.3700000047683716"/>

                    <GradientStop Color="#e4ffffff" Offset="0.6299999952316284"/>

                    <GradientStop Color="#c6ffffff" Offset="1"/>

                </GradientStopCollection>

            </LinearGradientBrush.GradientStops>

        </LinearGradientBrush>

        <Style x:Key="AxisThumbStyle1" TargetType="ig:AxisThumb">

            <Setter Property="Width" Value="12"/>

            <Setter Property="Height" Value="22"/>

            <Setter Property="Canvas.ZIndex" Value="1"/>

            <Setter Property="Cursor" Value="Hand"/>

            <Setter Property="IsTabStop" Value="False"/>

            <Setter Property="Background" Value="{StaticResource BaseColorBrush}"/>

            <Setter Property="BorderBrush" Value="{StaticResource BaseBorderBrush}"/>

            <Setter Property="Template">

                <Setter.Value>

                    <ControlTemplate TargetType="ig:AxisThumb">

                        <Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="1,1,1,1" Background="{TemplateBinding Background}" CornerRadius="2,2,2,2">

                            <Grid>

                                <Rectangle Fill="{StaticResource BaseOverlayBrush}" RadiusY="1" RadiusX="1"/>

                                <Rectangle RadiusY="1" RadiusX="1" Stroke="#FFFFFFFF"/>

                                <Border BorderBrush="#FFFFFFFF" BorderThickness="0,0,0,1" Background="#FF99A6B2" HorizontalAlignment="Center" Margin="0,5,3,5" Width="1"/>

                                <Border BorderBrush="#FFFFFFFF" BorderThickness="0,0,0,1" Background="#FF99A6B2" HorizontalAlignment="Center" Margin="2,5,0,5" VerticalAlignment="Stretch" Width="1"/>

                            </Grid>

                        </Border>

                    </ControlTemplate>

                </Setter.Value>

            </Setter>

        </Style>

    </UserControl.Resources>

    <Grid x:Name="LayoutRoot" Background="White">

        <ig:XamTimeline Margin="28,44,97,73">

            <ig:XamTimeline.Axis>

                <ig:NumericTimeAxis ThumbStyle="{StaticResource AxisThumbStyle1}"/>

            </ig:XamTimeline.Axis>

        </ig:XamTimeline>

    </Grid>

</UserControl>

You can use it to make a custom one.