I live in Paris, and while I think it is certainly safe to wear your jewelry most of the time I would be careful. People don't have as large engagement rings here so it can stand out. Ideally, I think you should only wear your pieces when you go out for a nice dinner and keep them in the hotel lockbox the rest of the time. If you are in an extremely nice area (think 9eme, 4eme, 8eme, 16eme, near Parc Monceau 17eme) you will stand out less, but there have been more incidents of burglary even around there recently so it's a risk. Better yet, get copies made and wear those (what I did for my engagement ring).