Hi Can,
To change to the "SIDEBAR" text in the Off-canvas sidebar, please open the "templates/t3_bs3_blank/tpls/blocks/off-canvas.php" then file the following code:
<div class="t3-off-canvas-header"><br>
<h2 class="t3-off-canvas-header-title">Sidebar</h2><br>
<button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button><br>
</div>
Now change to "Sidebar" to any text you want.
P/S: you can change the sidebar icon also, please check the documenation:
http://www.joomlart.com/documentation/purity-iii/faqs#sidebar-icon
Gardner.