The design appears in In Lebor Ogaim, or "The Book of Ogam," and is listed as one of the "cryptic varieties" of ogam. Both the translations of "window" and "ridgepole" bring to mind the notion that you can "look through" the fege (ridgepoles in Iron Age houses tend to lead to the smoke hole at the top of the roof), so we put a hole in the middle of it, since it's just empty space, anyway, and it is kinda cool to think about "looking through" the ogham, especially in this configuration. Religion, after all, is all about orienting yourself, and having the ogam as markers of your vision is pretty darn cool.
erynn999's book, Ogam: Weaving Word Wisdom, has a section on this (p. 144 in my edition, which I think is the current edition). She has some very interesting thoughts on the subject (including some notions regarding the shamanic process of "climing and squeezing out through the roof-hole" that are terribly worth considering). She describes the "ridgepole" in question and the hole at the top like this:
"The Féige Find can be immagined as the tree the poet climbs upward into the center to reach imbas and the Otherworlds. The glyph itself, with its five concentric rings, can be seen as the roof of the hut when you lie on your back looking up to the rings and thatching and the central smoke-hole. The ogam feda themselves are like the bindings that hold the thatch, and the stars spinning in the night sky around the central post of the world tree, or the north star that is the nail about which the heavens revolve." -p. 145It's damn good imagery.
Anyway, I spent some time last night doing some practical work with the fege, as last night was our usual bit of Clergy Order Work. I meditated with the Window up to my closed eye, centered on the flame of a candle before me, and when I opened my eye and looked through the Window to the candle flame, I saw things beyond the flame before me that were reflected in the vision I had been meditating on. The real interesting thing was that I had left a pad of paper on the working space before me (so I could write things down afterward, not during, though I'd already drawn the fege on the paper), and I almost immediately had the urge to begin writing. Words poured out of me for a little bit. I had drawn the fege find on the pad before the journey, and found myself writing four sets of words in the four corners around the outside of the fege, and a fifth set of words spiraling through the fege itself.
When I went to journal the experience, I had to re-translate the words, which was not terribly easy, since I had been writing from one position, so some of the words were written backwards. I did manage to understand everything I wrote, though (sometimes by re-tracing the words in reverse to figure out what letter I'd intended to write). All the sets of words (couplets, almost) were about fire and poetry. It was a strange but deep experience.
This version is done in cedar, because we like working in cedar, and it burns very cleanly (as opposed to some other woods that don't always burn well). We might try some other woods, but we'll have to see (oak, for instance, burns very poorly when it comes to detail like this. The most interesting thing is that apparently, no one has ever thought to make these things into jewelry, it appears, and we do love doing things that are new and unique! You can pick one up at The Magical Druid, of course!