Leonard Nimoy got the Vulcan hand sign from a Jewish blessing.
For a 1967 episode of Star Trek: The Original Series Leonard Nimoy’s Vulcan character Spock was to, for the first time in the series, appear with other Vulcans. He decided Vulcans would have their own greeting that isn’t a human handshake or bow. Nimoy thought back to his childhood and remembered an Orthodox religious service he attended. The Jewish Kohanim performed a blessing where they brought their hands together, thumb to thumb, and parted their fingers between their middle and ring fingers (forming two Vs). This hand sign forms the Hebrew letter Shin which is the first letter of “Shaddai”, one of the names of God.
Nimoy took this two-handed blessing and turned it into the one-handed Vulcan salute. This gesture is often accompanied by one of the most famous phrases from Star Trek, “Live long and prosper.” When the “Amok Time” episode aired the hand sign instantly became famous. People would make the sign to Nimoy everywhere he went. Many people thought it was just a fun variation on the peace sign but unbeknownst to them they were (in a way) actually blessing one another.