Use trash bin icon,

and add tooltip to checkbox

IPython/html/static/tree/js/notebooklist.js

@@ -264,6 +264,7 @@ define([
         if (selectable !== undefined) {
             checkbox = $('<input/>')
                 .attr('type', 'checkbox')
+                .attr('title', 'Click here to rename, delete, etc.')
                 .appendTo(item);
         }
 

IPython/html/templates/tree.html

@@ -41,7 +41,7 @@ data-terminals-available="{{terminals_available}}"
                     <button title="Duplicate selected" class="duplicate-button btn btn-default btn-xs">Duplicate</button>
                     <button title="Rename selected" class="rename-button btn btn-default btn-xs">Rename</button>
                     <button title="Shutdown selected notebook(s)" class="shutdown-button btn btn-default btn-xs btn-warning">Shutdown</button>
-                    <button title="Deleted selected" class="delete-button btn btn-default btn-xs btn-danger">Delete</button>
+                    <button title="Deleted selected" class="delete-button btn btn-default btn-xs btn-danger"><i class="fa fa-trash"></i></button>
                 </div>
                 <div id="new-buttons" class="btn-group">
                   <button class="dropdown-toggle btn btn-default btn-xs" data-toggle="dropdown">