This came up on another sub and I answered that the name on their birth certificate would give them away, but that was a barely-educated guess on my part. Note, I absolutely believe the Holocaust happened and in no way hold the victims responsible.
edit: title should be "Jews in 1930s Germany," sorry.
Someone else may come along with more to say, but there is a very good answer here
This will hopefully get an answer in this thread (since I believe it's been a few years since it was answered on this sub with anything other than a reference to a previous question), but this and similar questions have been asked before, so I'll link to a roundup of a few of the best answers from a few years back.