His age was beginning to show, his one sign of inner turmoil, the strong line of his jaw melted a little, one became aware of telltale creases forming under his ears, one noticed not his jet-black hair but the gray patches growing at his temples.
There are no more uses of "telltale" in the book.
Show samples from other sources
But not before I see telltale redness in his eyes.
Sabaa Tahir -- An Ember in the Ashes
Connor waits for the telltale sting of the tranq bullet but it never comes, because the moment the bullet is fired, the boy in white takes a step back, and he’s hit in the shoulder.