The circle(or sphere) as a symbol of the self:

It expresses the totality of the psyche in all its aspects, including the relationship between man and the whole of nature. Whether the symbol of the circle appears in primitive sun worship or modern religion, in myths or dreams, in the ground plans of cities, or in the spherical concepts of early astronomers, it is always points to the single most vital aspect of life- its ultimate wholeness.

In the visual art of India and the Far East, the four-or eight-rayed circle is the usual pattern of the religious images that serve as instruments of meditation.

In terms of psychological symbolism, it expresses the union of opposites-the union of the personal, temporal world of the ego with the non-personal, timeless world of the non-ego. Ultimately, this union is the fulfillment and goal of all religious: It is the union of the soul with God. The two interpenetrating triangles have a symbolic meaning similar to that of the more common circular mandala. They represent the wholeness of the psyche or self, of which consciousness is just as much as part as the unconscious.

The square or rectangle:

If the circle is a symbol of the psyche(even Plato described the psyche as a sphere), the square(and often the rectangle) is a symbol of earthbound matter, of the body and reality. [Source]

Some tests to take:

Symbols Test

Personality Test (this is me these days)