free shipping label

[kinslayer]

I would like to add free shipping label, if the product have free shipping attribute.
 
Similar like new label is added in product-list.tpl
 

{if isset($product.new) && $product.new == 1}
<a class="new-box" href="{$product.link|escape:'html':'UTF-8'}">
<span class="new-label">{l s='New'}</span>
</a>
{/if}

 
How can I check, if product have free shipping attribute or not ?