A transmutation circle is a sigil or sign for a specific magical purpose. The sigil combines a complex combination of symbols and text to reach a goal or purpose as predetermined by an alchemist.

What does a transmutation circle Do?

The circle becomes a catalyst for a desired power, allowing the character to change items at will. The transmutation circle has also become a popular design for tattoos, allowing the wearer to keep a personal power close to him or show that he is a fan of the manga series.

What does a transmutation circle say?

So basically what they transmuted was a lifeless body which then inherited Alphonse's soul. The meaning of the circle is simply that: to bring about creating life through alchemy which typically results in the creation of a homunculus.