Determine if current item's PlaybackController is the main window's PlaybackController?

I’ve got a Smart Client plug-in that overlays information over a specific camera feed. I want to restrict the overlay to windows that are being controlled by the main window’s playback controller. Is that possible? Any helpful hints to help me figure it?

Another way to ask: Is there anyway to find out if the window I’m running in has been “linked” to the main window?

I have consulted Milestone Development but unfortunately there is no way to do it.