using System;

using System.Linq;

using System.Collections.Generic;

​

public static class StringExtensions

{

   public static string GetInitials(this string value)

      => string.Concat(value

         .Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries)

         .Where(x => x.Length >= 1 && char.IsLetter(x[0]))

         .Select(x => char.ToUpper(x[0])));

}

​

public class Program

{

    public static void Main()

    {

        var list = new List<string>(){"James blerg Smith", "Michael Smith", "Robert Smith 3rd", "Maria splutnic Garcia", "David Smith", "Maria Rodriguez", "Mary Smith", "Maria Hernandez"};

        foreach(var name in list)

            Console.WriteLine(name.GetInitials());

    }

}