functions.php

<?php

/**
 * Admin Label
 *
 * @author Bill Erickson
 * @link http://www.billerickson.net/fun-avatars/
 *
 * @param array $classes, list of all classes
 * @return array $classes, list of all classes
 */
function be_admin_label( $classes ) {
  $comment = get_comment();
	if ( $comment->user_id > 0 && user_can( $comment->user_id, 'manage_options' ) )
		$classes[] = 'byadmin';
 	return $classes;

}
add_filter( 'comment_class', 'be_admin_label' );