The Leningrad Codex contains sixteen decorative geometric patterns of medieval Jewish art. One of them, the cover page, shows a Star of David in a square while the square is in a circle. There are Hebrew verses from the Bible around the star and the square, and in the center of the Star there's a dedication of the book to the writer's teacher.
The Leningrad Codex is the oldest surviving complete copy of the Masoretic text of the Hebrew Bible, written by Shmuel ben Ya'akov in Egypt in 1008.
Photo courtesy of Wikipedia entry: Leningrad Codex