Hashirama's forehead seal.
Hashirama's forehead seal, that circumpunct, is actually the Bindu symbol.
We all know that Kishi tends to use histoy, eastern mythology and Buddhism while creating characters, storylines and symbols. Bindu, is an actual symbol from the olden schools of Tibetan Buddhism. It represents a vast number of things, but mainly; creating life from nothingness.
Bindu is said to be located at the back of the head. This centre is said to be where the chakra is produced from, a chakra that can be the nectar of immortality.
In metaphysical terms, Bindu is considered to be the point where creation begins.
In most books the Bindu chakra is not mentioned, but in the Tantra teaching a lot is written about the healing and rejuvenating effects of said chakra. It's basically considered to be the health centre of the human body and when put to use, it's said to speed up healing, satisfy the being both physically and spiritually and basically grant the user immortality.
In the ancient scriptures, it's said that the awakening of Bindu chakra triggers the pineal gland which produces Amrita, the nectar of immortality. The scriptures follow by, claiming that just one drop of Amrita is sufficient to make new shoots grow on a piece of dry wood, and bring the deceased back to life.
As a result; Bindu chakra is mostly associated with healing, regeneration, rejuvenation, plantation and creating life. It's said to be achieved by pure consciousness and greater awareness. The symbol used to describe it is the same as Hashi's forehead seal. A dot inside a circle, the circumpunct.
Anyways, thanks for reading.
Credits to: Kirin Rei