We can set a margin to an annotation.
<UserControl
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:Custom="http://schemas.microsoft.com/surface/2008"
mc:Ignorable="d"
x:Class="FingersDance.Views.TimelineAnnotationView"
xmlns:vw="clr-namespace:FingersDance.Views"
x:Name="UserControl"
d:DesignWidth="640" d:DesignHeight="480">
<UserControl.Resources>
<vw:ThicknessSingleValueConverter x:Name="myThicknessSingleValueConverter" x:Key="myThicknessSingleValueConverter"></vw:ThicknessSingleValueConverter>
</UserControl.Resources>
<Grid x:Name="LayoutRoot" Margin="{Binding Path=TcBegin, Converter={StaticResource myThicknessSingleValueConverter}}">
<Rectangle Fill="Green" HorizontalAlignment="Left" VerticalAlignment="Top" Width="4" Height="20"/>
<TextBox Text="{Binding Path=GestureType}" Width="100" Margin="5,0,0,0"/>
</Grid>
</UserControl>