[blind-eddie]

Create the plugin as stated above, name it Subscribed.
Hook Location, select, showthread_query

In the Plugin PHP Code message area,
Add:

$hook_query_fields .= " ,subscribethread.*";

$hook_query_joins .= " LEFT JOIN " . TABLE_PREFIX . "subscribethread AS subscribethread ON (subscribethread.threadid=post.threadid AND subscribethread.userid=post.userid)";

In your postbit or postbit_legacy template find:

		<if condition="$post['signature']">
		<!-- sig -->
			<div>
				__________________<br />
				$post[signature]
			</div>
		<!-- / sig -->
		</if>
<br><br><br><br><br><br><br><br><br>

Add below:

                                <div align="left">
                                <if condition="$post['subscribethreadid']">Subscribed</if>
                        </div>