<Window
x:Class="WafClient.Presentation.Views.SampleWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:u="clr-namespace:WafClient.Presentation.Behaviors"
ResizeMode="NoResize"
u:WindowBehavior.HideCloseButton="True">
...
</Window>