I recall one of the very first card counters who I ever spotted was back when I was a dealer in my local casino back in the very early 1990′s. The only blackjack knowledge that I had at that time was when I had read Beat The Dealer by Edward Thorp.
But that book was more than enough for me to be able to spot any conventional card counter and certainly one who wasn’t making any effort to disguise his play. We actually went on to become very good friends and still are to this day.
One of the things that gets counters spotted is the intense concentration that they exhibit when they go about their job. This is a dead give away as is looking at the discards. When a counter looks at the discards then what they are trying to do is to calculate the true count. In another post on the same subject, I mentioned how not converting the running count into a true count was one of the biggest mistakes with regards novice card counters.
To better estimate the true ratio of high cards and aces to low cards then you need to divide the running count by the number of decks remaining to be dealt. This is why a counter often looks at the discards. However it is a mistake to look like a counter as if anyone in the casino has this knowledge then your playing life is going to be cut severely short.