Kiowa

 Hadley: "This is their true sign and refers to a former practice of clipping the hair above the right ear to show off ear ornaments. The motion has been mistaken for a circle, but it was not originally." (p.103)

Seton: "..because they used to cut their hair on that side to show the ear ornaments or ear painted red." (p.108)

James Mooney seems to be the greatest expert on the etymology of this sign:

"To make the sign for "Kiowa" in the sign language of the plains tribes, the right hand is held close to the right cheek, with back down, fingers touching and slightly curved, and the hand moved in a rotary motion from the wrist. According to the Kiowa this sign had its origin in an old custom of their warriors, who formerly cut the hair from the right side of the head, on a line with the base of the ear, in order better to display the ear pendants, while allowing it to grow to full length on the left side, so as to be braided and wrapped with otter skin after the common fashion of the southern plains tribes. This was in addition to the ordinary small scalplock hanging down behind. This style of wearing the hair, although now nearly obsolete from long association with tribes of different habit, is still occasionally seen. It is shown in the picture of the chief Big-bow, taken in 1870."

“You know, everything had to begin, and this is how it was: the Kiowas came one by one into the world through a hollow log. They were many more than now, but not all of them got out. There was a woman whose body was swollen up with child, and she got stuck in the log. After that, no one could get through, and that is why the Kiowas are a small tribe in number. They looked all around and saw the world. It made them glad to see so many things. They called themselves Kwuda, "coming out." The Way to Rainy Mountain, N. Scott Momaday