I think you can find the Magen David symbol in the ancient mosaics in Eretz Yisroel. I can’t really say that is a good proof, though, since you can find some other symbols there, too. Perhaps not all of them were so Frum. Also, the Gemara says that if a non Jew made one of the images that we are prohibited from making, you may Daven there. I doubt that applies to the Jupiter images though.
Yesterday, I saw a Tshuva from Reb Moshe. The questioner asked if he is Mechuyav to rip off the Magen David from the Paroches, since as we all know, it is Avoda Zara Mamish. Reb Moshe replied that although he doesn’t know the significance of the symbol, while he does suggest one, it has been on Perochos for centuries — long before Zionism. All of our greatest leaders had it in their Shul and it never bothered anyone.
Actually, in one of the Heimishe papers, a few years ago, there was a supplement about old Shuls of Europe. In the picture of the big Shul of Satmar, you can see a nice Magen David on the outside of the Shul.