Around 17<sup>th</sup> century, Sicilian ships began to use a simplified variant of the traditional kingdom flag, whose design had been purely heraldic so far. Thus, the new flag became horizontally divided into three stripes of equal width; being white with a Sicilian eagle the upper and lower stripes, while the central one was in turn divided into four alternately yellow and red stripes. Such design survived as official until 1816, despite the abundant political changes suffered by the island, until its abolition by the King of the Two Sicilies. Even after losing its official status, it continued to be used until the unification of Italy.
Sources: Flags of The World (FOTW) website:Sicily Historical flags (Italy) | Wikipedia(it):Bandiera del Regno di Sicilia
Sizes: ensign W12 x L18 mm, mast flags W8 x L12 mm, jack W6 x L9 mm, pennant W4 x L48 mm.