using System;

using System.Text.RegularExpressions;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var lastline = @"{E\ansi\RTFDATA\E\rtfl\E\ansiSIGNED ELECTRONICALLY by John Smith\RTFDATA}||||||F|||20220502213000";

        var regex = new Regex(@"[A-Z]{3}");

        var matches = regex.Matches(lastline);

        foreach(var match in matches.Cast<Match>())

        {

            Console.WriteLine($"Matched on: {match.Value}");

        }

    }

}