using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        string str = "*!#©™®";

        var regx = new Regex("[^a-zA-Z0-9_.]"); 

        if (regx.IsMatch(str))

        {

            Console.WriteLine("Special character(s) detected.");

        }

    }

}