gistfile1.phtml

<?php


function is_protected_post( $post_id = NULL ) {
  global $post;
  
  if ( $post_id === NULL )
    $post_id = $post->ID;
  
  foreach ( array(Memberful_Post_ACL::PRODUCT, Memberful_Post_ACL::SUBSCRIPTION) as $check ) {
    $manager = new Memberful_Post_ACL( $post_id, $check );
    $acl = $manager->get_acl();
    
    if ( ! empty( $acl ) )
      return true;
  }
  
  return false;
}

?>

<?php if(is_protected_post()): ?>
<img src="..." />
<?php endif; ?>