The Nautical Star is an old symbol used by sailors. It represents the North Star. If a sailor was stuck without any kind of navigation system, the stars were always a way back home. If you could find the North Star - you could find home. Sailors, believing in curses and omens, often tattooed a Nautical star on thier forearms to ensure a safe journey home.
Later, the Nautical Star was used by soliders for the same reason.
They are also used today as a symbol of independance and finding one's own way in life.