Hmmmm, that is weird. The first thing I'd try to restore that Mobile data icon is tapping that 'Reset' button. (...and then you'll probably have to re-juggle the icons you want in your Notification bar.)
If that doesn't work, maybe try going into your Settings >> Application manager and then slide over the 'All' menu. Scroll down to 'Touchwiz home', select it and tap the 'Force stop' button, then the 'Clear cache' button. Restart your S3 and hopefully that icon will be back.