3391 Sinon is a Jupiter Trojan asteroid that orbits in the L4 Lagrangian point of the Sun-Jupiter system, in the "Greek Camp" of Trojan asteroids. It was named after the Greek hero Sinon, who was a warrior during the Trojan War. It was discovered by Hiroki Kosai and Kiichiro Hurukawa at the Kiso Observatory in Japan on February 18, 1977.