Here are the Celts, depicted shamelessly, buying villagers from the Sherif of Nothingham to use as slave warriors. You gotta have a dot in a triangle of course, it's mirrored, who cares. To my limited knowledge that is not a Celtic symbol. At least Finn, on the right, gets redeemed somewhat at the end.
Here Robin and the Celt escape the prison tower with a Pyramid parachute. You know, outlaws going down the pyramid.
"Villagers are dying across England, the only thing the people have is a spark of hope called Robin Hood, he's an idea, something the people can believe in..." Doesn't that sound familiar?