Book module do not display icon for book and chapter print. Acctually these icon are generated but the browser do not display them becasuse they are overlayed but "Turn editing on" list item.
The solution is to edit book/tool/print/ and change the empty string parameter on lines 51 and 53 to something meaningfull. I suggest folowing changes to lib.php code.

line 51
$booknode->add(get_string('printbook', 'booktool_print'), $action, navigation_node::TYPE_SETTING, null, null, new pix_icon('book', '', 'booktool_print', array('class'=>'icon')));

line 53
$booknode->add(get_string('printchapter', 'booktool_print'), $action, navigation_node::TYPE_SETTING, null, null, new pix_icon('chapter', '', 'booktool_print', array('class'=>'icon')));