on his/her face
Lo sguardo sul suo volto era impagabile.
The look on his face was priceless.
Le mutande della vittima sul suo volto, come con Hyang-sook.
The victim's underwear on his face, like with Hyang-sook.
— Memorie di un assassino (2003)
Giudicando dall'espressione sul suo volto, lei era preoccupata.
Judging by the expression on her face, she was worried.
It's written on his face.