The problem as I see it is that I always want to show a high enough card so the captain will be more likely to park the boat in a more interesting and challenging spot. Unfortunately, that depends on everyone else showing high cards as well, AND that information actually being passed on to the captain. I have been on boats where it seemed like the operation didn't take the time to bother assessing the overall diving level of the load - which is very frustrating to me.
The thing you don't know is what card the captain or DM might be looking for. As has been mentioned earlier, some DM's don't know what to look for - which on a personal level I don't understand. If one takes being a DM seriously at all, it's not that hard to go on the internet and discover that there is more out there besides just padi! In fact, it's actually interesting!
So on one hand, since a pro card seems to be the most universally respected "highest level" (possibly ignorantly in some cases), one is tempted to show that. On the other hand, the fear of disclosing your professional level and being included in a lawsuit that you, other than randomly being there, had nothing to do with, makes one reluctant to disclose professional certification.
A representative of one of the other agencies recently told me he never discloses his pro level on vacation dives - to avoid being included in random lawsuits. He said random inclusion actually happens more often than you might think. So it sounds like
@MargaritaMike 's experience is not unique, and his advice sound. What I didn't realize until Mike's post is that plaintiffs are able to discover professionals amongst the uninvolved from just their 'diver' certs on the manifest?! That sounds like some sort of privacy violation to me, so it would be interesting to know how that process works (anyone know?). I suppose maybe the solution to protecting discovery of professional certification might be to show your highest diver certification from an agency you are not a member of? Or maybe your NAUI card that has no cert number ...
It seems like the cards are stacked against the advanced diver getting to dive advanced dives - at least on open boats. The only sure fire way I know of to get advanced boat parking is to charter it yourself, or go on someone else's advanced charter ...
cheers