Don't be a fucking pussy!
You've no wife or kids, so nothing to lose apart from a bit of face in front of your mates, and you think none of them do this either? You can never be sure.
As Frank says, if she has a bit of brain, she'll offer discretion as a part of her service. She should have as much interest in keeping things hush hush as you do.
Should you see her, the accepted protocol is if eyes meet, a very subtle acknowledgement that she is there, a slight smile or similar. If she turns away, you leave well alone. She's with people that she doesn't want to have knowing. You never know. She may give you a big beaming smile and rush over to chat or give you a peck on the cheek. If the latter occurs, take it on face value and don't make the mistake of some silly twats and think you're on a date. You ain't. You've just bumped into a friend/acquaintance. Act like that is the case.
It's happened to me on a number of occasions. Usually the polite nod does the trick. One two occasions I ended up having drinks with the girl and her mates. By sheer coincidence I was a trusted enough punter to know both of these girls' real names and so it looked totally natural speaking to them and having a laugh.
Even when asked by one friend of a girl "so how do you know each other, we knew enough very basic details about one another to make that seem entirely natural. What DID get awkward is when the same friend who asked how we knew each other took a bit if a shine to me and asked for my number.
I had to decline. THAT would be seriously crossing the line and would make the (working) girl in question very uncomfortable.
You've not got a lot to lose. If you live your life in fear, it will be miserable.
