When I add the gallery code to an article, I don't see a image gallery I just see the text:

I installed plugin_jw_sig-v1.2.1r2_j1.5 on joomla 1.5.15. I didn't get any errors during installation. I even tried using the Simple Image Gallery with a fresh install of Joomla but I get the same non-working result (as shown in the image attached).

I am using a local XAMPP install (Windows version 1.7.3), but I also get the same result online with BlueHost.

I have also read this thread (apparently others are having problems too) but no answers yet.
forum.joomlaworks.net/index.php?topic=4158.0

I already have <jdoc:include type="component" /> in my template

Turns out there was a simple fix in my case. When I installed the plugin it was disabled by default (see screenshot attached).

Go to Extensions > Plugin Manager and look for "Simple Image Gallery Plugin". Make sure it is not disabled.