The Leningrad Codex (or Codex Leningradensis) is the oldest complete manuscript of the Hebrew Bible in Hebrew, using the masoretic text and Tiberian vocalization. It is dated AD 1008.
The cover page to this ancient text is obviously showing great prominence to a single symbol- the Hexagram (Magen David). Thus, it is logical to conclude that the leading Jewish authorities at the time (1008 A.D.) deemed it to be a sacred religious icon- kosher enough to be included as the cover page for the Hebrew Bible. Therefore, to say that the Star of David has been a religious symbol of Judaism for at least 1,000 years cannot be easily denied.