By dropping your own icon with the same name as the Liferay icon, your icon will appear as the bookmark/favorites icon instead of the Liferay icon.
The icon is located under:
/Your_Theme/html/themes/example/images/liferay.ico
See http://wiki.liferay.com/index.php/How_can_I_change_the_Liferay_bookmark/favorites_icon%3F