MCCarran Airport to be exact. While waiting in a ticketing/check in line, a huge line that snakes back and forth, I spotted a provider that I knew well. Knew her really well, as she had me calling her by her real name and I had even been over to her place and met her kids. Anyway, she was in the adjacent section of the line, and as the line moved we were heading toward each other, so we were going to pass within a couple feet of each other. I observed her for a while to see if she was alone, and sure enough she was. Now, if she had been with someone, I wouldn't have said a thing, but since she was alone I said hi, and she said hi back, and we had a nice, pleasant, brief conversation that two friends would have that ran in to each other in this way.
Had another "in public" encounter while living in Las Vegas. This time at a bagel shop. I was paying for my bagel and coffee when I heard a female voice call out "Hey (my name)." I turned around and saw a woman, alone, wearing big sunglasses, that I did not recognize. She then said "It's (her name)." After she said her name, I quickly realized who she was and said hi. This particular provider I had seen only once and spoken to at a couple of the meet and greet parties, but she obviously recognized me. We sat down together in the bagel shop and had a nice conversation including catching each other up on the local gossip. We even agreed for her to come over to my place that evening for some fun!
In each of these situations the ladies were alone. Should I ever come across a provider "in public" that was with someone else, I wouldn't make an attempt to contact her. If, by accident, we should see each other, I would just smile and leave it at that, unless she initiated some sort of contact.