The belief that demons exist and furthermore can possess an individual is mostly seen as the stuff of fiction and horror films— but it is also one of the most widely-held religious beliefs in the world. Most religions claim that humans can be possessed by demonic spirits (the Bible, for example, recounts six instances of Jesus casting out demons), and offer exorcisms to remedy this threat.
The idea that invading spirits are inherently evil is largely a Judeo-Christian concept; many religions and belief systems accept possession by both beneficent and malevolent entities for short periods of time as uncommon — and not especially alarming — aspects of spiritual life. Spiritualism, a religion that flourished across America in the 1800s and is still practiced in a few places today, teaches that death is an illusion and that spirits can possess humans. New Agers have also long embraced a form of possession called channeling, in which spirits of the dead are said to inhabit a medium's body and communicate through them. Hundreds of books, and even some symphonies, have been allegedly composed by spirits.
- Quote : http://www.livescience.com/27727-exorcism-facts-and-fiction.html
 There are many symbols for possession and also anti-possession which are commonly known even if the their true identity isn't.