I noticed over the past few days that a little green square has appeared next to my name. At first I could see a green square next to everyone's names (every time they post), but now it's just my own, with a little link saying 'add to reputation'. How come I can only add to my own reputation?

I can see the green square in peoples' profiles, but nowhere to add reputation. I'm guessing this is some kind of work in progress?