If you can't post the image, I advise you to try to find an Art historian in your area. Even if he does not have the answers to your questions, he will know where to start the researches.
Also, if the painting is framed, you can try to remove the frame (be very careful to not damage the painting !!! Maybe ask a professional) because sometimes the signature is hidden by the frame, or is in the back of the painting.
Good luck! :-)