This symbol is inscribed on a fountain pen from the 1940’s (a Skyline Executive, so it might have been a presentation pen). Here’s a photo, or you can see the symbol in a photo here on eBay, scroll down to the listing, click on the 4th photo and use the built-in magnifier.
Here is also a description:
It consists of a circle, and contained within the circle is a square, the points of which touch the inside of the circle. There is also an isosceles triangle the base of which is congruent to the base of the square, and the top point of which extends outside the square and even a small distance outside the circle. In the middle of all this, centered horizontally but slightly below center vertically is a capital letter T.
It appears to be a variant of the alchemical symbol for the philosopher’s stone but the rectangle and triangle have different relative sizes than they usually would, and I don’t know what the T is for. Under magnification it looks quite precisely and professionally incised, so I have to suppose that the relative sizes of the different shapes are intentional.
I would say the ‘triangle’ is actual a compass (as in the arc drawing tool not the thing that points north) based on the detail at fulcrum point, so presumably a Masonic remembrance of some sort. I would guess that the ‘T’ probably represents a particular branch/lodge/whatever, but no idea what those divisions are or how they identify.
Any detail you’re seeing at the top of the triangle, I’m afraid, is an artefact of the photos, under 10x magnification I can see it is just the top of a triangle being interesected by a circle. Also I can see the bottom of the triangle, not quite congruent with the bottom of the square, as I thought, it is actually resting on the bottom of the square.
The triangle-square-circle motif is fairly common, sometimes it refers to “squaring the circle” as a logical impossibility, and as I said, another version with a smaller circle in the middle refers to the philosopher’s stone. That’s why this reeks to me of some kind of secret society or occultism. I thought it might be something that someone would have seen before, but maybe not. Or if it’s a secret symbol of something perhaps those who know what it is are sworn not to tell. I hope I’m not opening the gates of hell (or the Bill Gates of Hell) by trying to find out.
For what it’s worth, I made four sketches of the logo in MS Paint: with and without the T, black on white and white on black. I did an image search on them all on both Bing (the only thing it’s good at) and Google. I didn’t get any useful results.