<?php
// put this in your application
function add_header_comment($tpl_source, &$smarty)
{
    return "<?php echo \"<!-- Created by Smarty! -->\n\"; ?>\n".$tpl_source;
}

// register the postfilter
$smarty->register_postfilter('add_header_comment');
$smarty->display('index.tpl');
?>

  

The postfilter above will make the compiled Smarty template index.tpl look like:

<!-- Created by Smarty! -->
{* rest of template content... *}