In my experience, it all comes down to how much you bet when you are betting large, i feel the threshold of tollerance is around 150 dollars/hand+/- the parnoia of the casino. If you are playing at a 5 dollar table, and your betting 50-75 dollars, nobody will care unless your really blatantly counting cards by counting aloud, or asking the dealer what the index for your current hand is.
Also, the simple fact that you sometimes bet ten dollars and sometimes bet 150 dollars is the biggest flag of all that you wave saying "i might be a card counter"
I just walk up to tables sit down, not betting at all, then place only bets of one predetermined size for every bet i place, then the only way they could know im counting cards is if they figure out why im not playing every hand. Ivs had far less heat/backoffs playing this way