First Appearance: Tales of Asgard backup story in Thor #131 (1966)
While I first thought this item was The Eye of Agamotto (described below), it turns out it's The Warlock's eye, a mystical weapon in the comics stolen by Thor and the Warrior's Three from Harokin, an Asgardian enemy of Thor.
The Eye of Agamotto (Not this, unfortunately)
First Appearance: Strange Tales #115 (1963)
Created by Marvel comic artist Steve Ditko, The Eye of Agamotto is based off of the real-world item known as "The All Seeing Eye of the Buddha," a symbol from Nepal which offers the powers of good luck, fortune and protection to its owner.
In Marvel Comics, this mystical item is one of Doctor Strange's amulets and is named after Agamatto, a previous Sorcerer Supreme.
In the Marvel movie universe, this item is yet another easter egg, potentially leading to a tie-in with the Dr. Strange movie currently in development.