User can subscribe to any feedback or forum changes.
Users can subscribe and monitor needed feedback or forum. Just click on "Subscribe" link in right panel.
It's a very good feature, however it is hard to guess that the "notifications" block below "forums" block actually manges topic subscription. It looks more like forum/user wide setting to me. Also tip doesn't help. As a quick fix you may want to change tip to "...receive notifications on this topic". Later you may consider moving it somewhere to the top or to the topic menu.
Customer support service by UserEcho