What artifact does Ky give to Cassia when she thought he would be returning her compact?

The next morning, the world feels much better. The storm is gone. When they go hiking, Ky presses something into her hand. She thinks he is returning his compact. He runs off ahead of her, and she feels disappointed. She feels as if something is lost when he leaves her, but she reminds herself that she has gained something, too. Her compact is back. When she is alone in the woods a few minutes later, she notices that Ky didn't give her compact back. It's a different artifact that is the same size as her compact. It says N, E, S, W, and there is an arrow inside the letters. The arrow spins and points back at her. She wonders why Ky gave it to her.