The Hand of Saruman, otherwise known as The White Hand, was the primary symbol of Saruman's Orcs towards the end of the War of the Ring. The hand was featured prominently on their banners, and used as an intimidating symbol on their helmets and faces.
Portrayal in adaptations
In Peter Jackson's The Lord of the Rings film trilogy, the mark is created by Orcs dipping their hands in white paint-like substance, and applying the paint on each other's helmets. The hand is well known to their enemies, proven by Éomer's quick recognition of it as of the First Battle of the Fords of Isen.