Can you please tell me who the non-signatory states are to the Geneva
Conventions?
The Geneva Convention relative to the Treatment of Prisoners of War has been in force since 21 October 1950. It is easier to answer who HAS signed the Conventions since the International Committee of the Red Cross keeps an updated list of States party to the Geneva Conventions and their Additional Protocols. By looking at this list of signatory states, you can figure out who HASN'T signed it.
You may also be interested in the Society of Professional Journalists' Reference Guide to the Geneva Conventions that includes a brief history of the conventions and a list of online resources and links to organizations working in the area of human rights.