Bindable Converter Parameter

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel;
using System.Timers;

namespace BindableConverterParameterTake2
{
    class MainViewModel : INotifyPropertyChanged
    {
        public MainViewModel()
        {
            _FirstName = "ABC";
            _LastName = "DEF";

            Timer t = new Timer(2000);
            bool state = false;
            t.Elapsed += new ElapsedEventHandler((s, e) =>
            {
                if (state)
                {
                    ConcatSign = "-";
                }
                else
                {
                    ConcatSign = " ";
                }
                state = !state;
            });
            t.Start();
        }
        private string _FirstName;
        public string FirstName
        {
            get { return _FirstName; }
            set { SetProperty(ref _FirstName, value, "FirstName"); }
        }

        private string _LastName;
        public string LastName
        {
            get { return _LastName; }
            set { SetProperty(ref _LastName, value, "LastName"); }
        }

        private string _ConcatSign;
        public string ConcatSign
        {
            get { return _ConcatSign; }
            set { SetProperty(ref _ConcatSign, value, "ConcatSign"); }
        }




        private void SetProperty<T>(ref T field, T value, string propertyName)
        {
            if (!EqualityComparer<T>.Default.Equals(field, value))
            {
                field = value;
                var handler = PropertyChanged;
                if (handler != null)
                {
                    handler(this, new PropertyChangedEventArgs(propertyName));
                }
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;


    }
}