Throughout The Lord of the Rings, "the Eye" (the Red Eye, the Evil Eye, the Lidless Eye, the Great Eye) is the image most often associated with Sauron. Sauron's Orcs bore the symbol of the Eye on their helmets and shields, and referred to him as the "Eye" because he did not allow his name to be written or spoken, according to Aragorn (a notable exception to this rule was his emissary, the Mouth of Sauron). Also, the Lord of the Nazgûl threatened Éowyn with torture before the "Lidless Eye" at the Battle of the Pelennor Fields.
fonte: Wikipedia
