Apparently, with research, that symbol apparently is apparently the basic shape for Alchemy:
To quote, "This simple 17th century "sign" illustrates the blending of geometric shapes, elemental symbols and astrological signs. Each part representing the various "elements" and forces needed for magical work in the quest for physical transformation and spiritual illumination and immortality. Many medieval alchemists based their philosophies on mystical traditions rooted in the Kabbala
(Jewish mysticism), Hermetic magic
and the occult practices
of ancient civilizations such as Egypt and China. See Philosopher's Stone and Phoenix
Your best bet is to look at occult symbols, the real alchemy and the Sefira (if I'm not wrong) of the Kabbalah.
...If...you put it in FMA terms and see how the Philosopher's stone is made and connect it with that illustration...it suddenly makes sense.
I'm going to take it apart:Circle
means heaven/unity/perfection/womb. God is everywhere and nowhere.Triangle
means fire, if we put it in Kabbala terms or religiously, the triangle represents The Father, the Son and the Holy Spirit. The Mind, The Body and The Spirit. If I'm not wrong, the Father. (an upside down triangle is female)Square with a circle inside
This explains it better than I could:
The circle in the square represent heaven and earth coming together (a great temple symbol) (also in China's terms from what I gathered). The heavens are often described as a bowl and often symbolized by a circle. In paintings, God is often depicted as laying out the heavens with a compass and the earth with a square. The square is made with a square and represents the earth which is often described as having four corners. The temple is a place that represents the union of heaven and earth, and where heavenly beings (Angels & Jesus Christ) literally come. TLDR
It's the symbolism of heaven and earth united.
Then add in the images of God, humans, and it suddenly makes sense.
Overall, I believe that symbol/emblem means either immortality or rebirth. mostly immortality.