Ouroboros: An ancient symbol frequently used in alchemical illustrations to symbolize the circular nature of the alchemist's opus. Often represents self-reflexitivity or cyclicality, especially in the sense of something constantly recreating itself.
Vegvisir ("the viking compass"). It is said that if this sign is carried, one will never lose one's way in storms or bad weather, even when the way is not known. It is encircled by protection runes. This would be a cool tattoo.