I have just read on worldbiking.info that they got one bicycle and some panniers nicked while in Bolivia. And a few hours later a friend of mine asked me what do you do when you want to eat, visit a museum or do some food shopping.
Luckily cycle touring is very safe, the amount of tours I have read about on blogs and in books I have lost count on, but I can only remember a very few thefts. And these thefts are often just a bag, camera and some money while you are at a restaurant, not the whole lot.
It is really not while you are on tour you have to be worrying since you will be be away from populated places. Such as at 1200m wild camping overlooking a lake and you haven't seen anyone for hours or even days.
It is when you are around other people and common sense goes a long way to keeping your gear safe.
We have parked our bicycles outside Dubrovnik in a hidden corner in the parking lot, while we had a lovely walk about and a yummy lunch in side the walls. Though thinking about it we should probably have done the same as the French couple we spotted and have parked them closer to the gate and in sight. As our bikes were hidden and therefore also hidden for someone who wanted to find out what we had in our bags. Though hiding in plain sight might not work too.
It always depends on when and were you are, so as my mum always says "stick your finger in the ground". What we do is send on person to the toilet, shops etc at the time, park the bicycles right next to us if we are eating in a restaurant.
Though these "tea-leaves" are crafty little buggers so even when you are standing right night to your stuff, even holding onto it, they will find a way to relive you of your worldly goods.
Some tricks are to not wash your panniers, time will also help, as dirty and worn bags will look like there isn't anything of value in them. Asking at a shop or the security/ticket office at the place where you are visiting, you will many times find that it is ok to park it where they can keep an eye on it. Old dirty knickers I have heard works well too :)
It is good to carry a lock but while touring though weight is and issue, so we tend to carry a thick Kryptonite cable with a pad lock. Which works great to lock the frame and even the bags to something. Ok as all cyclist know if they want it, even with the strongest D-lock out there, the thieves will get your goodies. But any lock will deter any opportunist who will just grab and go.
TravellingTwo again trumps my blog post with their post - Bike Security & Locks For Bicycle Touring. A very good read and we have gotten some great ideas on how to keep our stuff safe on our tours from that article.
Other useful links :