It's a brand new feature for community administrators (which is why there's no FAQ about it yet). You have to choose to mark your entries or your comments 'as admin'. It's not automatic. If you're beta testing the new post entry page it's in the Entry Flags box (you may need to edit your settings to see it) and in a comment you have to see the ?reply page so click on more options I think (there's another suggestion below mine to make that easier to get).
Here's what it looks like to give you an idea: http://experiment.dreamwidth.org/18481.html