Yes, you can already do this.
First, make sure you have your settings set to automatically subscribe you to threads you post in. That's in UserCP --> Edit Options
http://www.dnforum.com/profile.php?do=editoptions
under "Default Thread Subscription Mode", make sure thats set to
anything other than "Do not subscribe".
Then, on the thread listing pages, you will see this image if you are subscribed already:

That should give you exactly what your looking for, yes?