Csharp/C Sharp by API/System.Windows.Forms/MessageBoxIcon

MessageBoxIcon.Exclamation

 
    using System;
    using System.Windows.Forms;
    
    public class MessageBoxShowExclamation {
        static public void Main()
        {
            MessageBox.Show ("Hello, C# World!", "Howdy",
                       MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
        }
    }