Mvvm - how to capture in the viewmodel and the parametercommand classes, which UI button was pressed?

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MVVM

To simplify, Criticized for writing a novel in another forum w/no code a month ago, I made a quick Wpf project (uses MVVM) with 2 buttons on the UI. When a button is clicked, I need my ViewModelBase and/or ParameterCommand classes, to know which UI Button was clicked. So I can route the Speech Synthesizer to the correct Text to Speak. Thanks 4 any help!!

<Window x:Class="Wpf_School_Announce.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Wpf_School_Announce"
        xmlns:vm="clr-namespace:Wpf_School_Announce.ViewModels"
        mc:Ignorable="d"
        Title="Announcements" Height="236.436" Width="293.218">
    <Window.Resources>
        <vm:ViewModelBase x:Key="viewModel"/>
    </Window.Resources>
    <Grid DataContext="{Binding Source=viewModel}">
        <StackPanel Margin="0,10">
            <Button x:Name="btn1stBell" Content="1st Bell" HorizontalAlignment="Center" VerticalAlignment="Top" Width="75" Margin="0,10" 
                     Command="{Binding ParameterCommand, Source={StaticResource viewModel}}" 
                    CommandParameter="{Binding Command, ElementName=btn1stBell}"/>
            <Button x:Name="btnLunchMenu" Content="Lunch Menu" HorizontalAlignment="Center" VerticalAlignment="Top" Width="75" Margin="0,10"
                     Command="{Binding ParameterCommand, Source={StaticResource viewModel}}" 
                    CommandParameter="{Binding Command, ElementName=LunchMenu}"/>
        </StackPanel>
    </Grid>
</Window>


namespace Wpf_School_Announce.ViewModels
{
    public class ViewModelBase
    {
        public ParameterCommand ParameterCommand { get; set; }

        public ViewModelBase()
        {
            ParameterCommand = new ParameterCommand(this);
        }

        public void ParameterMethod(string <Not sure what needs to go here>)
        {
           Debug.WriteLine("Parameter Comand:{0}", AnnoucementModel);
            //Todo: Need to find out which UI button was clicked to direct The Speech Synthesozer to the correct Speech Text.
        }
    }
}

namespace Wpf_School_Announce.ViewModels.Commands
{
    public class ParameterCommand : ICommand
    {
        public ViewModelBase ViewModel { get; set; }

        public ParameterCommand(ViewModelBase viewModel)
        {
            ViewModel = viewModel;
        }

        public event EventHandler CanExecuteChanged;

        public bool CanExecute(object parameter)
        {
            return true;
        }

        public void Execute(object parameter)
        {
            ViewModel.ParameterMethod(parameter as String);
        }
    }
}

What I have tried:

I have tried using CommandParameter="{Binding Source={StaticSelf ElementName}}"