Chricky said:Harp is for Leinter, Red hand is for Ulster, Connacht is a wing and an arm with a sword I think and Munster is three crowns on a blue background
Those signs are pretty modern, and don't represent traditional Gaelic symbology, except for the hand and the harp. The three crowns of Munster come from Henry II, who made John Lackand lord of Ireland with this three-crowned coat of arms (although they could probably be based on the three kingdoms of Munster). The Connacht eagle-and-arm dimidation is probably spanning from Western "given" heraldry. There's a theory about a German monastery connected with the kings of Connacht, but it doesn't seem plausible. I'd say they were the XIVth Century arms of some Norman lord (the eagle) and some Celtic tradition (the arm).
The Red Hand, though, is a very traditional Celtc symbol. Cutting enemy hands was a common practice among them. Probably, an enemy hand on a shield was its origin. But that's just my guess, it could have been anything. The same for the harp, found for the first time in the banner of Owen O'Neil, in the XV-XVIth Centuries.
Considering that the High King of Ireland at the time is Brian O'Neil, the ensign of the Ua Néill clan would fit better. It's the Red Hand, as far as I know.