best you minimize contact as casino mgmt
may think you are his associate...
Thus, if you seen with a counter, you risk being made as one also...interact minimally, just like any two tourists might.
Blackjack literature often says that only one in a hundred people playing blackjack in a casino can count... but I personally think that quite a few people playing blackjack know something about counting...but for a variety of reasons only a few are successful at it long-term. i expect everyone to know a little about counting, so I treat everyone like a tourist would. I suspect everyone else is doing the same--playing the game i call "keeping the big secret".
But let's say you have spotted one really good player that you are sure is a solid counter. Usually a nod, a wink or some other gesture is enough to communicate "i am a counter too and i will keep your secret if you keep mine." Indeed, counting is only part of your skills you need to play winning blackjack--the craft of playing undercover is the challenging part!
Generally, if you are at a table with a counter, it looks bad for you both...indeed, you move your bets in unison up and down with the count...that isn't good for either of you and makes it easy for the pit to make you both as counters. If it is a place you want to play frequently, give up your spot as soon as you can (that is when the count tanks or the start of the next shoe--in hand held games, after the 2nd time the count goes up high). If you go there seldom, say only once a year or twice a year, fire away.
But lets say you are backcounting, and want to wong-into a table that another counter is playing at. Many counters don't like Wongers-in coming in to eat up the high counts and your counter may say something if you mid-shoe enter his table more than once in his session...its a risk you would have to take. I would do it once, maybe twice, but no more (after all, i counted the table, and I have as much right to play as anyone).
The counter should play two spots on high counts if he thinks there are other likely to mid-shoe enter. And if a counter notices your wonging-in on him consistenly, he might even put you to use (or to express it colorfully, pimp on you)...he could ask you to bet some money for him in your circle (overseas he would back bet you), or he could wait for you to wong-in at another table, then come to that same table to wong-in as well (piggybacking on you as his spotter!)
As you can surmise, there are lots of sneakly little dramas that can play out on the casino floor...indeed, gambling, like anything else involving money, can reveal a person's character faster than anything else.