This man explains something about the tradional thing, though it seems to go back long beyond the Jewish tradition.

Pretty good. I have a book comparing the Indo-European ans Semitic languages written by Professor Saul Levin. While we're on Jewish liturgy and hands, there is an instrument one uses while reading the Torah scroll in temple called a yad 'hand' (in Hebrew, also the name of the letter). It is in the shape of a hand withe index finger extended. Rather than put one's real finger under the words as you are reading, you use the yad.

Ceci n'est pas un seing.