I am reading the Phil Leonetti book and they use that term.

Scarfo and Leonetti are Calabrian last names; but they are both related to each other.

In the Leonetti book Phil would say how his uncle would claim you "can't trust 'siggies'".

In that line of work or business, I don't think you would want to trust anyone too much.

Some Calabrians do have Sicilian ancestry, or vice-versa as they both would marry each other.

I looked up Italian-American slang, and they have this term on the link below it.

sigilian’ – Sicilian (siciliano)

http://xeroth.wordpress.com/2009/04/14/italian/

I have an Italian friend from Genoa. I showed her that site and she said that with some Italian-Americans they use words that are based not on Italian but the local dialects. Or some can be regional slang like in Philadelphia and other cities in the Northeast they call marinara sauce "gravy".

The comments on the slang blog page are interesting.