Well, Brandon, I can think of one very widespread hand signal for swearing, and I sincerely hope that it is not an
official part of Sign Language!

I can think of 'Mama mia' and 'oy veh'(sp?), but I'm not sure these count as swearing. P'raps Emanuela can help.
I expect most cultures have had some form of swearing by their god or gods, or something holy to them. "By the wrath of Zeus", possibly, and I seem to recall from long ago reading that there was a saying, "By the Oracle at Delphi". In Mary Stewart's Merlin series, she has King Uther swear "by Mithras", and numerous characters swear by
various gods.