The tattoo on Björk's left arm is the Vegvísir, a word that literally translates into "sign post." While often confused for a Viking symbol, it's actually from the 16th-17th century Icelandic book of magic called Galdrabók. Some of the spells in the book are protective, meant to prevent illness and suffering, and others are intended to cause fear, kill things, seek out evil, cause flatulence, or turn women into witches. The Vegvísir was used to prevent people from getting lost in harsh weather.
A manuscript from the 18th century reads: "If this sign is carried, one will never lose one's way in storms or bad weather, even when the way is not known."
Bjork also has a tattoo of a star behind her right ear. When asked about that, she said it was "just for fun."