For example, here's a post of how they used the rune Algiz:
Here's the link to the page with this particular blurb, and you can easily see the rest of them, there are tons: http://spn-symbols.livejournal.com/It would make perfect sense that among the several sigils, seals and symbols to call out whatever thing that dragged Dean out of Hell, there would be some protective symbols too.
The Algiz symbol, also known as the "Rune of Watchfulness" represents protection, assistance, defense, warning, support in adversity. It may also indicate a spiritual helper or guide. It is used in magic to make hunting more successful*, although I don't think it means the same kind of hunting as the Winchesters!
It is associated with the Norse myths of Heimall, a protector and guardian who watches the gates between worlds and who holds his sword in one hand and his horn in the other guarding the divine realm of Asgard.
There is a variety of other attributes associated with Algiz, including some that really fit the Supernatural mythology story line and characters:
- Mystical and religious communication with non-human sentient beings
- Reversed: vulnerability and sacrifice without gain. There are people who deceive and mislead you and may you become the scapegoat for the failures of others. (x)
- Algiz signals that protection may be expected from an outside source in a conflict that is either forthcoming or is already ongoing.
Bobby had painted the rune at both ends of the barn. You can see it next to the doors that Castiel enters and at the back where Dean learns who had gripped him tight and raised him from perdition.