We have spent many weeks in France on 3 trips. There were times we had to lock the bikes with all panniers on them in order to sightsee. We had no problems. If you worry about it too much, you will end up not seeing all you want to see and spoil the trip. Lock them up in a busy public place if possible. Many times, we stopped and camped in places we wanted to spend a day sightseeing so all our gear was in our tent and we only had the bikes to worry about.