<ControlTemplate x:Key="InputErrorTemplate">           
            <DockPanel>
                <Ellipse DockPanel.Dock="Right" Margin="2,0" 
             ToolTip="Некорректные данные"
             Width="10" Height="10">
                    <Ellipse.Fill>
                        <LinearGradientBrush>
                            <GradientStop Color="#11FF1111" Offset="0" />
                            <GradientStop Color="#FFFF0000" Offset="1" />
                        </LinearGradientBrush>
                    </Ellipse.Fill>
                </Ellipse>
                    <AdornedElementPlaceholder />
                </DockPanel>                     
        </ControlTemplate>