If you see another advantage player (AP), basic protocol is to get away; leave, do not even make eye contact. I'm of the mind that the AP who was at the table first has that territory, but since that belief is not universal, it doesn't always work. When I was playing at lower stakes than I do now, if someone sat down on my game and the count was positive, I may have asked the other person to wait to play for a moment, spouting some nonsense like, “I have a lucky feeling and I've been waiting for some luck.” If they were rude or continued to play, I simply left the casino.
You can make friends through this site, but don't do it at the tables. You shouldn't say something and risk annoying a fellow AP just because you want to make contact. This may work out fine sometimes, but your advances will not always be welcome. Now that I play high stakes, I'll just leave. Another AP wonging in is so rare that I'll not give much up for the peace of mind and longevity.
I won't even start on the problems with being associated with another counter. Team play will quickly get you in a database. If either of your play has been watched, your player's club card has been flagged, or either of you are JDLR, you may both be under the same surveillance microscope.
This is the stuff that freaks me out. I have less fear of casino employees than I do of another counter. I don't think I'm alone in this. It may be exciting to see another counter, but please contain yourself. It does seem like we do this in a solitary world and some think its "cool" to identify another counter or other AP. However, don't act upon your desires -- show some self control.
I've had a green-chip player and a red-chip player both say something to try to make contact. Once I see comportment skills that are this bad, I just leave. I do have to say that the other person is not in real danger from physical violence from me, but my main thought is to choke the inconsiderate player who is behaving inappropriately. I often wish it were like the movies where you could just knock them out, they fall and no one takes notice.
I'm very passionate about this. I got nailed at a profitable casino because a red chipper couldn't keep his mouth shut. He thought it was cool to make contact. He was being watched and after he tried to catch up to me as I left the casino, I was put under surveillance. The casino shift manager is now an acquaintance. A week later when he backed me off, he specifically told me that the other counter drew attention to me.
The databases (Griffin, OSN, Biometrica, etc.,) contain ploppies and civilians who were just talking or being friendly at a table with a suspected AP. Don't screw up something for another person who may not feel the same as you about wanting to make contact.