Cool! Those look like Greek letters on the faces. Greek letters are also numbers, of course. Via io9.
According to Bertrand Russell, the D12 (he calls it by another name, of course) was the last (fifth) regular polyhedron discovered, and that the Pythagoreans kept it secret and gave it mystical significance. Our word “quintessence” is related, I believe.
The ancients associated the D20 with the sky and Zeus. There’s also a D20 inside that blue liquid in your Magic 8-ball.
For a twenty-minute discussion on the D20 and its algebraic group, listen to Atomic Moocast #25. My bit begins around the fifty-minute mark.