Eye Symbol

ALttP/ TotG
The eye symbol has been seen throughout the Zelda series ever since the release of A Link to the Past/ Triforce of the Gods. In that game, the evil wizard Agahnim has the eye symbol on his robe and throughout his lairs. The symbol has lashes on the top and bottom and the inside circle is so thin that it almost appears feline.

OoT
The symbol appeared again in Ocarina of Time, when it was the symbol of the Sheikah, the shadow folk of Hyrule. They placed it all throughout their Shadow Temple, and on their artifacts such as the Lens of Truth, the Gossip Stones, and the Mask of Truth. They also placed it on their clothing, usually over the heart. The symbol has three triangular lashes on top and a tear drop on the bottom.

FS/ FSA/ TMC
During Four Swords, the evil wind demon Vaati is seen as personifying the symbol with his one stylized eye. It was seen again during Four Swords Adeventure and the Minish Cap, during which he acually had an exact copy of both the Sheikah style and Agahnim style eye on him in the final battle.

TP
The most recent appearance of the symbol would be with the Twili in Twilight Princess. It can be found on their artifacts, such as Midna's helmet and the Fused Shadow. It is also seen on their buildings and in places such as above Zant's throne.