This is another one that does not require any extra command or syntax.
Simply enter the UPC code into the search frame (leave out the spaces) and the first of the responses should read "Look up UPC number X XXXXX XXXXX X" where the X's represent the UPC code that you typed in.
Source: http://www.usrbingeek.com/a/000564.php
Main Page --> Google Stuff --> Looking Up UPC Codes