Grant that Tracy R. Rich is not right about all this, by the way. I have thoroughly researched this beyond JewFAQ.org, which I should note also has a Haredi P'rushi bias. Meanwhile, for example:
A lot of the surnames that sound Jewish to Americans are simply German names such as Klein, Gross or Grossman, Weiss or Weisman, Rosen, Schwartz or Schwartzman, Segal, Siegal or Sagal, and anything that contains berg, stein, man, thal or bluth. German surnames are very common among American Jews, and many people seem to have inferred the converse: if most Jews have German surnames, then most people with German surnames must be Jews. The reasoning is appealing on a gut-level but logically flawed. Consider this absurd but logically identical argument: most Jews have ten fingers, therefore most people with ten fingers must be Jews.
"Siegal" and other variants may actually be like "Katz"- variants or acronyms of kohein, kohen, etc. Also, "Levy" and other variants are, with perhaps a 0.01% exception, always a variant of Levi (As I said, JewFAQ.org has a Haredi P'rushi bias, and Tracy R. Rich has no problem attempting to delegitimize Patrilineal and Messianic Jews.).
As for the following:
Russian and Polish surnames are also often assumed to be Jewish surnames, for example names ending in -vitz, -witz, or -sky. It is commonly believed that "-sky" is a Jewish surname while "-ski" is not. This spelling difference, however, seems do have more to do with the source of the surname: Russia or Poland. The correct spelling of this common surname suffix in Polish is "-ski", and Poles usually kept that spelling after immigration to America. In Russia, this suffix is spelled in the Cyrillic alphabet, , and may have been transliterated into English as either -ski or -sky. However, a Jewish friend of mine who comes from Moscow tells me that in Russia, names ending in were usually Jewish.
I can tell you that records from sources such as Ancestry.com and JewishGen.org show that Non (Non-цкий) could be and were Jewish as well. She also missed "cki", "czki", etc.
There are other disclaimers about Tracy R. Rich and JewFAQ, but the linked-to JewFAQ page is like Wikipedia: a good start and for at least some of the basics.