Giorgia's 'sign language'

I'm still partway through the movie (just saw the third scene in Sicily). But a few times, for 'A Chi' and 'sette' Giorgia made signs, I'm assuming for letters?, using some kind of hand gestures that included her face. For 'sette' she spun her two pointer fingers around one another and then drew her finger and thumb away from her right eye, for example. 'A Chi' was the song title in the bar at the train station for Matteo to put on the jukebox; 'sette' was for the number of the photo for Nicola to look at, as she was moving into the apartment.

How did Matteo and Nicola know what she meant? They both got her meaning after a moment. Is this an Italian thing that is commonly known, comparable to Morse code? Or was she making the shapes of the letters in a way that I couldn't follow? Or something else?