Signature is not getting removed when quoting (using quote.module)

Signature in not being removed using signature module with quote module when quoting posts/comments.
Here is my solution:
Replace:

<?php
//cleaning signature in comment/reply
  if ($form_id == 'comment_form') {
    global $user;
    if ($form['comment_filter']['comment']['#default_value'] == $user->signature ) {
      $form['comment_filter']['comment']['#default_value'] = '';      
  	}
?>

With:

<?php
  //cleaning signature in comment/reply/quote (if present)
  if ($form_id == 'comment_form' && arg(1) != 'edit') { // do nothing if editing comment
    global $user;
	if(!empty($user->signature)) {
	  // signature must be in th end of the comment
	  $comment_lenght = strlen($form['comment_filter']['comment']['#default_value']);
	  $signature_lenght = strlen($user->signature);
	  // get the signature from the end of the comment
	  $signature = substr($form['comment_filter']['comment']['#default_value'], $comment_lenght-$signature_lenght, $comment_lenght);
	  if($signature == $user->signature) {
        $form['comment_filter']['comment']['#default_value'] = substr($form['comment_filter']['comment']['#default_value'], 0, $comment_lenght-$signature_lenght);   
	  }
	}   
  }
?>

Tested on producion site :)