I was in Vegas recently walking through the corridor from the Encore to the Wynn. I saw a young lady, walking arm in arm with a distinguished gentleman. As they approached I took a quit look, didn't stare just a quickie. They were both smiling and enjoying each other's company. When I glanced I knew the girl. It was someone I had met on a couple of occasions, she is a very well reviewed girl here. We past and I kept on walking like nothing happened.  
Later that night I got a text from her, "Was that you I saw?" I said "yeah" and we talked alittle. The one thing she did was to thank me for not saying "Hi" or anything to show that I knew her. Of course that's like rule #1, discretion. I knew it, I wasn't going to put her in a situation where she had to explain who I am, although the guy would have figured it out.
Now Vegas being a small town guys are bound to see someone they know, or may see someone in an ad they saw...Hell I was once in an elevator with my date, and someone I knew happen to be in the same elevator with us..and not a word was said.
I guess we have to be discreet here, I know you're bound to see someone you know here or there and you might lose your senses but...be cool, don't be that guy.