Compass stars are also popular for this reason. The nautical stars were originally used by sailors to help guide their way as they sailed through the night. They relied upon the stars to protect them and bring them home safely.
A lot of soldiers get nautical stars for the same reason... protection. It is a symbol of protection and guidance. It was a very popular tattoo among sailors.
So a case could be made that the nautical star tattoo, or a tattoo of any star for that matter, would be a symbol of guidance. Now as time has passed the nautical stars represent the direction of one's life, for those of us who are not sailors but still need guidance.
Some say that if the nautical star is pointed upwards they have a higher outlook on life and so on.