Thank you so much Udo!
Trying to figure this out really puts the old gray matter in a knot!
So as near as I can figure.....Ferdinand was king of Naples from his majority in 1759 as FERDINAND IV .
While he was effectively king of Naples, the combining of Naples and Sicily as the TWO SICILIES was a long standing convention as these regions were one of the largest states of what became Italy in the unification of 1861.
It would seem likely that this schiavona (or its blade effectively) belonged to a loyalist to Ferdinand at virtually any point from 1759-1806 while he ruled as Ferdinand IV (as blade inscription denotes).
By 1816, he became Ferdinand I of the Two Sicilies.
Would be interesting to learn more on the use of the traditional schiavona as shown here being used far outside the Venetian context. It has of course long been held by many that these were typically confined to Venice and the Dalmatian guard units of the Doge.