Though Sicily may conjure up images of Don Corleone and his Hollywood progeny, you won't come in contact with the Mafia during your time in Sicily other than in the newspapers. The "Cosa Nostra," as the Italians sometimes refer to it (don't use the term yourself) is focused on its own business and poses virtually no risk to tourists.
Wandering through sleepy interior Sicilian hill towns like Corleone (yes, it's a real place) and Prizzi, you might be subject to some curious and guarded stares by the locals and feel the haze of a silent old-boy network, but nothing more than that.