words inside the nimbus

During a recent inquiers class, I was staring at an icon of Christ (the Pantocrator) while I listened to our priest speak about the Holy Spirit part of the Nicene Creed, and about the filioque. I began to wonder two things: A) why the letters were there, if it was a sort of stance against Arianism, a visible reminder of the humanity and divinity? and B) if icons had always been written including the letters in the nimbus, or if historically the letters were added after the upheavals. Sort of an unimportant thing to be thinking, I suppose, but I tend to get stuck on my curiousities.

In John 8:58 Christ says, "I tell you the truth, before Abraham was born, I AM!"

In the nimbus around the head of Christ, we see the Greek letters spelling the name which God first told to Abraham when asked who He was. "I AM" or "THE EXISTING ONE", even sometimes "THE ONE WHO IS".

There are some very early icons that do not have the letters in the nimbus at all. It seems, from what I can find to reference, that since the iconoclastic upheavals (in essece, the iconoclastic upheavals denied the full humanity and full divinity of Christ) the letters are a very important part of writing an icon of the Christ. With the restoration of iconography the presence of the letters-and also nine lines forming the cross within the halo- appear with more consistancy. They seem as important as the stars of perpetual virginity on the maphorian in the icon of the Mother of God.

These symbols have great theological and doctrinal importance. . Since icons are not written merely for decoration, I'd assume there are certain ways to write icons, and certain things that must be included. I wonder why sometimes "I AM" is omitted. I noticed that IC XC is almost always present (the first and last letters of the name of Christ, in Hebrew I believe).

Does anyone have further knowledge on the subject?