That sticker on the drivers door jamb is a nifty thing. I dont know what year your Bronco is, but my 96 has an "H9" for the axle code. When I looked it up, all of the lettered codes had limited slip. the numbered codes were open. In my case it is a 3.55 limited slip.
the only thing I don't know is if the front axle is also a limited slip.
as far as you having posi or not, check the door tag or diff tag. an open diff drives both wheels, provided both wheels are experiencing the same amount of traction (like driving straight down the freeway) when one wheel spins, the spider gears transfer power down the path of least resistance, which is why one tire spins. and just because you have a posi doesn't mean both wheels are going to spin together all the time. from my experiences, the factory posi especially, they don't really work when you're on a flexy trail or if one tire is way stuffed and is binding on your body.
My broncois a 96 I bought it in july with only 38,000 miles and well taken care of. I found the original sale paper and it said limmited slip and 3.55 gears. I had a 88 f250 and only one wheel would spin what is that called, if both wheels spinning are limited slip?