I was just reading a great idea for a way to help an honest person return your lost digital camera to you. Write out an index card with "If lost return to" and your contact information. Even just an email or cellphone number, if you're leery about putting your address on there. Take a picture of the index card, and lock the photo so it's always on your camera even when you erase your photos.
Won't protect you from the dishonest, but if you're lucky enough to have someone honest find it, you just might get your camera (and photos, which are more valuable!) back.