Symbols are a quick way to communicate often complex ideas. Religions, particularly esoteric ones, commonly employ a great amount of symbolism to represent their beliefs.
Alchemy wasn't just a quest to transform lead into gold: it was a quest to transform base things into greater, more spiritual things, including the elevation of the soul. Alchemists coded their notes in a variety of personalized symbols. Here is a collection of common ones.
Modern Jedi follow a largely personalized religion. As such, there are no widely accepted symbols for the religion as a whole. However, some organizations within the movement adopt symbols that represent some of the basic tenets of their faith.
Occult principles are almost by definition impossible to directly explain with words. As such,
occultists regularly employ graphic symbols as well as allegory to communicate beliefs to others.

Catherine BeyerOccultists associate a number of symbols with the planets. These include astrological symbols, which are still in common use today. They also include numerological magic squares, complex seals constructed for those squares, and sigils of the spirits and intelligences associated with each planet.
To see information organized by individual planets, please see: Saturn, Jupiter, Mars, the Sun, Venus, Mercury, the Mooon.
Neopagan faiths such as Wicca are influenced by cultures that were largely illiterate and/or by occult beliefs that stress the value of symbology. As such, visual symbols are often an important part of a neopagan's spiritual path. Visit the Paganism / Wicca Guide Site for information on symbols associated with a variety of neopagan religions.

Catherine BeyerEach
loa, or spirit, in Vodoun has its own set of symbols which are drawn in powder during ceremonies and then subsequently destroyed. Variations in different traditions has led in some cases to a multitude of images being associated with the same loa.
The Faravahar symbol is the most commonly associated symbol for
Zoroastrianism. While it's meaning has changed over the centuries, the image can still be found on ancient Persian structures.