To put it bluntly the addition of that icon seems like 'idiot proofing'.

I have seen it posted a few times in this thread that people miss the sense of uncertainty that came from exploring the world. Accidentally pulling aggro was the most amusing part of FFXI. For example wandering around areas in the Sky zone and someone casting a spell and bringing the house down on themselves was hilarious. Avoiding aggro in FFXI with the three distinct types of aggro was an art in itself and was a very enjoyable robust part of the game. Here it's artless at best and now tacky on top of that since they're announced as aggro with ridiculous large red icons (that people still aggro anyhow).

There should be no indication that it aggros at all. Try a little good old fashioned learning and go figure it out yourselves. Also... if you aren't sure a giant troll monster or a dragon is aggressive... uninstall the game. (yes, I'm aware there are grey areas where they might or might not be aggressive, to that I refer you back to "go figure it out")