That's "Biscione": it's the heraldic charge of the noble Visconti family (from which comes also the famous film director Luchino Visconti di Modrone)... a sea snake devouring a youngster. Although the meaning has slightly changed through the centuries and Biscione means "Big Biscia" or "Big Grass Snake".
It is one of Milano's symbols, of Alfa Romeo, of Inter Football Club and the originary logo of Canale 5, the first Berlusconi commercial tv channel, as well.
EDIT:
https://en.wikipedia.org/wiki/Biscione