<Application x:Class="CSharp.App"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    StartupUri="MainWindow.xaml"
    Startup="App_Startup"
    >
</Application>

using System;
using System.Windows;

namespace CSharp
{
    public partial class App : Application
    {
        void App_Startup(object sender, StartupEventArgs e)
        {
            // Parse command line arguments for "/SafeMode"
            this.Properties["SafeMode"] = false;
            for (int i = 0; i != e.Args.Length; ++i)
            {
                if (e.Args[i].ToLower() == "/safemode")
                {
                    this.Properties["SafeMode"] = true;
                    break;
                }
            }
        }
    }
}

<Window x:Class="CSharp.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Loaded="MainWindow_Loaded"
    >
  <Grid>


...


  </Grid>
</Window>

using System;
using System.Windows;
using System.Windows.Controls;

namespace CSharp
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        void MainWindow_Loaded(object sender, EventArgs e)
        {
            // Check for safe mode
            if ((bool)Application.Current.Properties["SafeMode"] == true)
            {
                this.Title += " [SafeMode]";
            }
        }
    }
}