TRIBAL SIGN
Right index finger rubbed briskly up and down along the back of left index finger. This is the generic sign for all tribes of Apache connection, including Apache proper, Navaho, Mescalero, Lipan, and Kiowa Apache. It is commonly interpreted to mean "knife whetters" or "whetstone people," and this is also the meaning of the generic term for Apache in most of the plains languages. It is possible, however, that this is a misconception of the original purpose of the sign, which may have had reference to a peculiar musical instrument found in various forms among the Pueblo and other Indians of the southwest. Clark says:
I have heard two distinct conceptions for this gesture, the Cheyenne claiming that the sign came from a peculiar musical instrument made from an elk horn, which produced weird-like sounds by rubbing it backward and forward with a stick, and the second (I do not remember what tribe gave me the conception) from a specially good whetstone which the Apaches made and used (Clark, 9).
In a personal letter to the author Grinnell states, on Cheyenne authority, that the sign "is not whetting a knife, which would be performed by one open flat hand on back of other flat hand, and not poor, which would be passing right forefinger down over back of left forefinger held vertically. The sign is said by the Cheyenne to refer to a musical instrument used in old times by the Apache. This instrument was played by passing the forefinger back and forth over the flat surface of the instrument, from which surface a tongue protruded, which, when struck, vibrated and made the sound, somewhat after the manner of the Jew's-harp."