Nazis mostly used anthropology to spot Jewish peoples. Even a few decades ago when Jews did not mixed into native western Europeans that much, they used to resemble distinct Afro-Semitic/Arabic/Azeri/Armenian features. So it was easy to differentiate them from native races of west-Europe.
Hitler & Nazis used to believe that Indo-Europeans or Eur-Asian Aryan race had the features that are opposite to Semitic features.
- Plain silky hairs
- light eyes
- proportional face
- deep eye-socket
- dolicocephalic skull
- tall body build
- thin lips
The following 2 examples will illustrate the features enlisted above.
- A native German Aryan
- An Indus-valley/Asian Aryan
Now back to Semitic features, as hypothesized by Nazis under Himmler.
For example: curly hairs, non-proportionate face, hook nose, joint or uni-eybrow etc.
If you examine even west-European origin blond/red-head Jewish person, you may still notice those features mixed in.
Let me give you another proof that is those racist neo-nazi scums online still portray Jewish peoples with such features in their derogatory memes:
So, the differentiation aspects were more of racial features than religious identity or anything else.