Tetragrammaton magen david at Templo de la Congregación Israelita Buenos Aires Synagogue is courtesy of Robert Pollack who published it on Flicker and it shows a Tetragrammaton surrounded by a Star of David surrounded by a circle.
Tetragrammaton in Greek means "The Four Letters"; it stands for the name of God which is comprised of four Hebrew letters (Yod, He, Vav and He).
Robert Pollack wrote to me:
It is a strong symbol, and one that suggests unity and interconnectedness. It always reminds me of an elaborate knot.