[nickcarraway]

I'm no expert, but it's from a priestly hand blessing based on the Hebrew letter shin.

Nimoy's father took him to an Orthodox sabbath when he was a boy, and that made an impression on him.

[Calvin Locke]

Nimoy describe that visit, saying the eyes are supposed to be closed during that blessing, and he peeked, seeing the rabbi’s hands outstretched that way.