Jews were self-segregating in germany. Marking jews have been done many times throughout history (look up judenhut), and there were plenty of jews who welcomed the star at the time. Jews and Germans weren't the best of friends even before Hitler showed up. If you've read Mein Kampf, you know that Hitler used to loathe the rampant anti-semitism around him, and that he considered himself above it.

Pretty ironic considering.