I read what Daniel P. Faigin wrote about the King David shield:
"Medieval Jewish texts spoke of a magic shield possessed by King David that protected him from his enemies. These texts claim the shield was inscribed with the seventy-two letter name of G-d, or with Shaddai (Almighty) or angelic names, and was eventually passed down to Judah Maccabee".
Trying on the WWW to elucidate who's behind these "Medieval Jewish texts" I stumbled upon Hashkafah.com where TheGrimReaper's brings the following wonderful legend:
"I heard (from Rabbi Reisman), that during Dovid's last battle against the plishtim (which was his very last battle), he was taken captive by Ishbi-Bnov. The Plishtim tried killing him, first by using an olive press to crush him. A nes happened and the ground underneath him caved in, allowing him to escape that particular way of dying. The plishtim then tried throwing him up into the air so that he'd land over their outstretched swords, but just then he was saved by Avishai ben Tzruya who said the Shem Hashem, causing Dovid to be suspended in mid-air. So four points on the star relate to the four directions (N, S, E, W) and the two stars going up and down are to commemerate the fact that Dovid was saved by miracles going down (being saved from the olivepress), and by miracles going up (being suspended in mid-air). (Shmuel 2, 21:15-17)"