I don't blame you for wanting to change that setting, back in Wiichat's hayday, I had 'bout 1000 messages in my inbox after a few weeks. :lol:
Hit Settings next to Log Out and My Profile, and check the large menu on the left. Find My Account, click General Settings under it, and find the Default Thread Subscription drop down menu, and select Control Panel Only. This makes it so subscriptions only show up on the CP, and in Subscribed Threads through Quick Links.