Just to clarify something from earlier in case it was badly worded. I was in no way suggesting that DIR divers do not make mistakes. I'd be the (very) last person to be able to claim that
I was objecting to the simple assumption that they are wearing kit that looks DIRish ergo they are DIR.
They were blatently behaving like tossers if they were kicking the coral apart, but a tosser is a tosser, regardless of who trained them.
So, to return to the question - how do you actually tell for certain, I'd bounce that back at you. How do you tell for certain someone in trained from by any agency. Guess you'd have to speak to them. DIR divers are allowed to speak to "lesser" mortals as long as we have obtained written permission from Florida first.