The one with the three legs and the woman's head (maybe a Gorgon?) in the middle. What is the significance to this? Was it created by the de' Hautevilles and if so, why? It looks about as un-Norman as anything I've seen.
This is not an in-depth answer and I'm not an expert. But it's been a few days without either appearing so I might as well chip in with what I know.
You're right in that it's not a Norman banner but nor was it used by the Kingdom of Sicily. What you're referring to is the modern flag of Sicily. It's roots are old (going back to the 13th C Sicilian Vespers) but I don't believe that it's ever been used to represent Sicily as a sovereign state.
As to the design of the flag, it uses the same triskelion as the Isle of Man but I couldn't say what the significance of this is.
I hope that's enough to help direct your own research.