In the Western occult tradition, each planet can be represented by a seal or diagram. The seal is based off of the planet's magic square, with the seal theoretically touching every number within the square, although in practice that is not always apparently the case.
The Seal of venus does not follow the convention of overlapping every number of the magic square of Saturn. Twelve squares are missed entirely: 3, 5, 7, 15, 19, 21, 33, 35, 36, 43, 44, and 47.
The Venus seal is structurally similar to the seal of Mars. In mythology, Mars and Venus are lovers and thus are a pairing. In an earth-centric cosmology (such as what occultists worked within when these seals were designed), Mars and Venus are the planets closest to the Sun, which holds a special position and role within the cosmology.
Read more: Structure of the Celestial Realm, and the Importance of the Sun
The specifics of why the seals of Mars and Venus are constructed as they are is much more elusive than for the other seals. Donald Tyson suggests that the upper symbol may be a "V" for Venus coupled with a equal-armed cross. That cross, along with the circle, crescent, are the three basic shapes used in the construction of the astrological symbols of the planets. This makes some sense because 7 is the number of Venus and is also associated with the planets because there are seven of them within this system. The cross, circle and crescent can also represent the Earth, Sun and Moon on their own.