Sorry, you're right, it is in products.tpl, but the code is:
Code:
{$products[product].productcode}
(notice the "s" as mentioned previously)
But I dont know why it wouldnt show. Im new to smarty as well, although I cannot find any logical reason for it not to show if you have entered it like that.
Im going to have a look at the php scripts as well, maybe its a query at the search engine that doesnt look for the productcode by default.
Note: just for the heck of it, could you try as above (without the product sku initial note and bold tags ?