Enochian Sigils

This is a type of magic that both Demons, and Angels have knowledge of. Hunter have a breif knowledge, but do not completely understand it. It really begins to stand out in season 4 of Supernatural.

It's Uses
There are many uses for enochian sigils.

Keep Angels Out
These sigils can keep angels out of the building. It is invisable to the human eye, but angels and spirits can see them. It is demons who mainly do this. This technique is first seen in Death Takes a Holiday, when Sam and Dean notice it painted all over the funeral home. Castiel later confirms to Dean that those runes keep angels out.

Sam and Dean are later forced to write it all over Bobby's house to keep out Castiel in The Man Who Would Be King. The get it right in The Man Who Knew Too Much.

Hide From Angels
With them, humans can hide from Angels and won't be able to be found. So far, no angel has been able to overpower this. Sam, Dean and Adam are the only humans known to have these craved into their ribs. This was first seen in Sympathy for the Devil when Castiel craves them into Sam and Dean's ribs to hide them from the angels.

Hide Presence
This is seen in Frontierland, when a injured Castiel paints a sigil on Bobby's wall to hide himself well he healed. It is believed that it hides angel presence from any other angel.

Also Checkout:

 * Angel Banishing Sigil
 * Angel Banishing Spell
 * Tulpa: Tibetan Spirit Sigil