One thing I've noticed about Germans is that they are often surprised when I assume that an American named Goldberg, Rosenthal, Friedman or Rosenbaum is Jewish. I don't know any precise statistics, but I'd be willing to bet that 95% of Americans named Goldberg are probably Jewish.* Yet many Germans, even fairly worldly ones, don't associate these names with Judaism.
I've had to explain the 'Jewish names phenomenon' over and over to Germans. My explanation, which I've given a couple dozen times, was based on a hazy recollection of something I once read in one of those things that consists of a bunch of pieces of paper glued together inside a cardboard cover. I decided recently to try to see whether I was right, and came across this informative website:
Before the 1800s most German Jews who lived in cities had already either a fixed surname, or a double name (examples for such double names: Amsel Abraham, Löw Baruch, Ascher Simon). On the country side, Jews were often recorded in German documents solely by their given name (examples: Abraham, David, Jakob, Seligmann). In older documents one may find references to “Jacob Jude”, “Isaac Jude”, “Abraham Jude”, Jude simply meaning “Jacob Jew”, “Isaac Jew”, “Abraham Jew”.
During the Emancipation, some government officials misunderstood the legislation, and demanded that even previously appropriate surnames should be changed. A number of such examples can be found in the Duchy of Baden: In the District Administration of Lörrach (Rötteln), even the “acceptable” surnames Bloch and Braunschweig were changed. There had been 14 families with the Bloch surname, and 7 by the surname of Braunschweig. None of them kept their old surname. The Braunschweigs changed their names to: Beck, Braun, Dornacher, Graf, and Keller. The Blochs adopted the following family names: Dietersheimer, Dornacher, Dreher, Geißmann/Geißmar, Kaufmann, Kirchheimer, Mock, and Weil.
A number of the official name change lists still exist in Germany, as well as other documents that can help clarify what a family’s surname was before the official name change, and reveal if they actually changed their surname or were able to hold on to the family’s original name. Birth registrations in Naugard, Prussia, for example, list a Nathan Friedländer with the added remark: “by the name Silberstein”. Some records show him as Nathan Friedländer Silberstein, while he only appears as Silberstein after 1821. Between 1800 and the 1820s many “double names” can be found in documents – usually they reveal the family's surname before the name change, however in a few cases the families had adopted a new surname they didn’t care for after a while, so they changed again…
Please note: Jewish families were required change their names everywhere in Germany. Subsequently many families who were not related at all chose the exact same surnames: if your family came from the same town as another family with the exact surname as yours, it does therefore not necessarily mean that you are related to that family! …
While some of the newly chosen surnames are the same as the surnames of their Christian neighbors, others reflect the sensitivities of Romanticism, leading many to think of such names as “typical Jewish names”. Plant names such as Mandelbaum, Rosenbusch, Rosenbaum, Rosenstihl, Rosenstock, Rosenberg, Weinstock, or professional names such as Goldschmidt, Krämer, Mahler, Eisenhändler, may come to mind.
There were however numerous German Christian families, especially so in East and West Prussia, who had carried the surnames of Rosenberg, Rosenbaum, Rosenkranz, Goldschmidt, Goldberg, etc. already for many centuries. It is therefore extremely important to research one’s family history carefully, and once again, not to jump to any conclusions simply based on a surname.
In other words: a “Jewish sounding German surname” does not necessarily mean that ones ancestors were Jewish if one’s parents and grandparents were Christians! The same applies to German surnames mentioned in Jewish surname databases. When entering those same names into a regular database, one will very likely come across the same names among Christian families.
To prove this point, here is another example of Jewish name changes in the early 1800s from the District Administration of Durlach, in the Duchy of Baden: 17 Jewish families lived in the village of Weingarten (plus 6 individuals who were not married). Before the name change there were 3 families with the surname Esaias, obviously relatives or brothers, however each of them changed to a different surname! Among the 17 families the following names were chosen: Bachmann, Bär, Baum, Blum, Fuchs, Hirsch, Holz, Klein, Krieger, Löwenstein (previously Löw), Meerapfel, Rose, Rothschild, Schmidt, Schwarz, Sommer, Stahl, Stein, Stengel, Weidenreich, Winter. While Löwenstein, Meerapfel, Rose, Rothschild, indeed sound like “typical Jewish surnames”, all of the other surnames are in most cases not “Jewish names”, with a large number of German families who already had carried those surnames for centuries.
* One of the benefits of learning German is being able to tell acquaintances or friends what their names mean in German. The Himmelfarbs, Goldbergs, and Rosenbaums are usually pretty happy; the Schwarzes, Kleins, and Totenbergs, not so much.