What is the symbolism of a moon tattoo?

One of the Twelve Symbols of Sovereignty (imperial authority), the moon is a symbol of heaven.

The moon is representative of the passive principle (Yin) to the sun's active principle (Yang). The moon in heraldry is always shown as a crescent, usually with the points turned down.

In Western Astrology The Moon is said to represent the feeling nature of the individual. It is the "planet" associated with Monday, and the Zodiac sign Cancer.

It is used to characterize the inner child, as well as the past and how we have been as individuals rather than how we are now.

Pagans use the Moon as a symbol of the goddess and her worship. The three aspects of the goddess Maiden, Mother & Crone are represented by the crescent moon with its points facing left, the full moon or full circle and the crescent with its points facing right respectively.