שShin

Walk past a Jewish home and you may see a small case fixed at an angle to the doorframe, with a single Hebrew letter on the outside of it: shin. Inside is a tiny scroll carrying the words of Deuteronomy 6, including the command to write these words on the doorposts of your house. The box worn on the head in prayer carries the letter too, embossed on both sides — with three arms on one side and four on the other.

The practice is real and living. The reading of the letter — that it stands for Shaddai, the Almighty, so that the house is marked by his name — is Jewish tradition attached to the sign. Every doorpost wearing this letter is wearing a tradition, not a translation.

When the kohanim — descendants of Aaron — pronounce the blessing of Numbers 6 over a congregation, they raise their hands and spread the fingers in a particular way: thumbs together, a gap between the second and third fingers on each hand, so that the hands together make a three-part shape. Tradition reads that shape as the letter shin, standing for Shaddai — the Almighty blessing his people through their hands.

This is the most widely recognized hand position in the world and almost nobody knows why. Leonard Nimoy, raised in an Orthodox Jewish home, watched the priests do it as a boy from behind his father's covering hands, never forgot it, and years later gave it to Mr Spock as the Vulcan salute. He told the story often and freely.

The blessing is Scripture. The hand shape is a practice; reading the letter in it is tradition — and it is the single most-travelled fact about any Hebrew letter.

Rabbinic tradition reads shin's three arms as Abraham, Isaac and Jacob — the three patriarchs, distinct and rising out of one root. The four-armed shin on the head-box of the tefillin has its own traditional readings alongside it.

A reading of a letterform, offered on its own terms as Jewish tradition. The square-script shape it reads is itself relatively late; the letter did not always have three neat arms.

Look at a relief map of Jerusalem and three valleys — the Hinnom, the Tyropoeon and the Kidron — come together south of the old city in a shape people have long said traces a shin. Readers who love this put it next to Deuteronomy's promise about “the place which Jehovah your God shall choose out of all your tribes, to put his name there”: the city marked with the letter of the Name.

This is a reading of a map, taught widely in both Jewish and Christian circles, and it is a reading — not a claim the text makes and not a fact about the letter. Held as a reflection, it is a striking one.