From Joomla! Documentation

Changed this because it's misleading. The method itself is a bit confusing because it seems to imply linking to a file through its parameter defaults but does not. JToolBarHelper assigns a custom class to the title. This allows the developer to hook in their own image via a stylesheet. See line 31 of /administrator/includes/toolbar.php --Bluebridgedev 12:17, 25 August 2011 (CDT)