I just talked to one of my brokers, and the answer is that yes, your stop loss orders are definitely visible.

They are not listed in the Bid/Asks, they are listed in the "Special Term Orders", for those people who have FULL Level 2.  So yes, that's like playing Texas Hold'Em except the other player can see your cards.

I figure it makes sense to use them if the volume on a blue chip stock is huge (e.g. Volesoft at a billion / day or something) - in that case nobody will pay attention to your stop losses.

But I get it now that putting in stop losses on a thinly traded penny stock is a mug's game.  Argggh.