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.
Know your Vegvisirs. I was drawing these, wondered why the different versions around the place. Nobody can figure out what Björks tattoo actually is, a Galdrabók one roughly done most likely vegvisir symbol