I do not remember having seen on this list a very simple and
efficient method: the (compulsory) self-registering of Jews
as such. This was the case for instance in France: in the
German-occupied part of France (about two thirds of the
territory) the law was enacted on september 27, 1940, and
in the temporarily "free" part, nominally ruled by the
so-called Vichy government, it was enacted on June 2, 1941.
You may read many more details for instance on the pages

http://www.geocities.com/Eureka/Park/3446/udsr87/juif.html (in French), or
on http://levendel.home.sprynet.com/brief.html (in French and
in English).

Of course, for those who did not comply with this law,
there were denunciations, etc.

Basile Ginger, CGJ
(Cercle de Genealogie Juive, International JGS in Paris)
http://www.genealoj.org

Searching for: GINGER (Yavorov, Brody, Kishinev), BLUMENFELD (Lublin,
Kishinev), PRISMAN (Kretinga, Liepaja), GRINFELD (Brody, Kishinev),
HIRSCHBERG (Jelgava), KLEIN (only >from Odessa
ish