The all-seeing eye, also called the Eye of Providence or Eye of God, has origins dating back to the Eye of Horus in Egyptian mythology. It has been adopted as part of the Great Seal of the United States, which shows the all-seeing eye floating on top of a pyramid. This can be seen on the back of the one dollar bill. It is often associated with conspiracy theories involving UFOs, the Illuminati or Freemasonry. It is also featured in the 2004 Disney film, National Treaure, and in J. R. R. Tolkien’s Lord of the Rings trilogy as the Eye of Sauron.
In cemeteries the all-seeing eye symbol is usually found associated with Freemasonry or the Independent Order of Odd Fellows, like the example here. The letters F, L and T inside the chain links stand for Friendship, Love, and Truth.
Photo: Fairmount Cemetery, Denver, Colorado
Cemeteries and Cemetery Symbols 
Just wanted to express my appreciation for the informative, interesting and well-rounded descriptions, and for the excellent photographic examples. The lighting is perfect, and really makes the imagery come through clearly. Thank you for the excellent work.
The image depicted on this stone should be labeled as belonging to the Independent Order Of Odd Fellows. There is no connection between the lodges of Odd Fellows and Freemasonry. They are separate entities. Both are outstanding service organizations with their own moral teaching methods and ritual.