I honestly think that buying mirorred sunglasses is pushing the paranoia a bit on hustlers, don;t you? I have always put my wallet (a reduced sized one) and passport in my front pocket. No one would have the ganas to lift them from the front pockets. Also, you can buy a little lock with key (about 1E) if you will be on the metro with a handbag that you must carry. For guys, just make sure your favorite Mont Blanc isn;t in your backpocket or in one of the outside jacket pockets.
BTW, mirrored sunglasses tend to be very dark.