In the situations you've run into, what constitutes a "solo" certification? Does it have to be a card that specifically says "solo" on it, or are there other advanced certification levels that would also be accepted?
When I first started diving alone in Southern California it never would have occurred to me that it might require a special certification or that it might bother someone. I did several dives alone on Maui and nobody ever said anything or even gave me a funny look (at least not that I was aware of). Once again, it never would have occurred to me. If it wasn't for ScubaBoard I still might not know that I am an outlaw.