The Subscriptions feature is unavaialble in the mobile forums versions. Which is odd, as any mobile device is perfect for a fast check-up if anything has been posted in threads that you are interested in. But you can’t check it fast on your mobile device, using the optimized theme, because it’s not supported.
Can we please have the notifications and threads subscriptions fully functional on mobile devices? Hardly a priority in the engine development pipeline, but it would be so much more convinient for people using their mobiles to check if the interesting threads got any updates.