Many players especially those used to looking for tells in poker may be confused with the name of the article. However, a tell in Blackjack happens when the dealer reveals the hole card when checking for Blackjack.
In case the dealer up card is a Ten and the dealer checks it for Blackjack you may notice special features in the way he checks.
This can happen only with a live dealer as no computer can make such a mistake.
If the dealers hole card is a small card (2-6) he may need some more time to ensure that the card is not an Ace and lift it a bit more.
If the card is a face card, the dealer needs just a second to see what it is. Therefore, if the dealer did not require much time to look at the hole card, it may be a face card or a card higher than 8.
There are a lot of books on blackjack tells that teach you how to reveal the secret tells and have higher winning chances.