In 4.03 In the Beginning, Mary Campbell is seen wearing a charm bracelet. The charms have various mystical significance, allowing Dean to identify her as a hunter. There are at least six, probably eight to ten, charms; including a human figure, possibly a Buddha or Kwan Yin. The other identifiable symbols are...
The unicursal hexagram is a six-pointed star that can be drawn in a single line. It is a common symbol of Thelema, the religion founded by Aleister Crowley (who is of course referenced in the names of the demons Alastair and Crowley.)
A version of this called the Aquarian Star is used by the Men of Letters as their crest which dates back to the Legend of Atlantis. When she was brought to the Bunker in 12.01 Keep Calm and Carry On, she told Dean that she knew about the Men of Letters, but she thought that they were a myth.
The cross is the most common symbol of Christianity. While originally the cross was a medieval instrument of torture used in crucifixions, it later became a positive symbol. Only a long-legged cross is Christian, an equal-armed cross predates Christianity by around 1500 years. While it is a protective symbol, vampire lore holds falsely that the cross deters vampires.
The pentagram was originally a Mesopotamian protective symbol and later a Pagan religious icon. In modern times, the Pentagram is used by Wiccans; when inscribed inside a circle, it is called a pentacle. Some devil's traps use pentacles. An inverted pentagram was later used as a Satanic symbol.