Think of it this way would you have liked her to say hi to you if she saw you with your wife or GF or group of friends. Then you had to explain how you know her.

Just kidding, but I had to do a double take because I always think this is going to happen to me, except that I'll recognize someone first (my facial recognition is above average I've noticed) and they won't recognize me and I'll proceed to play the hiding game!

And personally I'd rather stick to a subtle nod or hello of recognition if necessary, but definitely no conversation. Never know who each person is traveling with or knows in the surrounding area. I travel often for real work and have the "good" fortune of always encountering people I know in strange places.

lol that's kind of my dream scenario...

In general I would say etiquette says that you should not bring up anything out loud when accidentally meeting her in public.  I have been recognized in public and I found that the least creepy way that guys have asked me about it is by sending an email to my work account asking if they really did see me in X place and if so would I like to meet up with them?  The answer was no in one case because the guy was looking for OTC fun, but if he has actually been into paying my rate, I might have found it totally fun to meet up with someone who ran into me in public.  Another time I had someone hire me for an Outcall back to the same hotel I had visited earlier that day after seeing me walk thru the lobby of the hotel on my way out.  I guess the fact that I actually look as good as or better than my pictures convinced him LOL.

However... train sex is a specific fetish of mine.  So if any of you ever see me on the train and happen to have some spare benjamins in your pocket and want to do it in the bathroom... I'm probably down.  Just saying!  But let's be discreet please.  I ride the trains a lot and don't want to be banned or anything.  LOL.  I feel similarly about airports?  Something about doing the nasty in transit is just super hot, IDK why!  

I'm with the majority here, having had a similar situation once.  Turned out the provider recognized me too, as she later dropped me an email thanking me for not stirring the pot.

That said, then along came Zoey with her tempting reply.  I guess this is a YMMV deal; maybe I'll start asking ahead of time.  Could lead to some interesting times....

discussed this ahead of time since there is a possibility of crossing paths - we have a simple cover story to explain why we might be acquainted should we bump into each other.  Just in case.

If I happened to find myself sitting next to a lady I'd seen before, sure I'd discreetly say hello or smile at her. If she didn't recognize me or seemed in any way uncomfortable, I wouldn't push a conversation, and perhaps would offer to find a different seat if it would make her more comfortable (as odd silence can be uncomfortable).

i'm gonna be a dummy and respond

without reading anyone else's response....
wtf!
I think if I had met someone once or twice and sat next to them on a train & they didn't jar my memory, i'd be sad

"if you walk without rhythm you won't attract the worm"

lol
good luck with that one :