It's horrible to see how easy it is to open a LOCKED suitcase!
As seasoned travellers hubby and I came up with these ideas to discourage the would-be-thief (TWBT) from targeting your suitcase:
1. Use suitcase that has a built-in lock on it and use your normal lock in addition.
This type of suitcase has a fixed point where you can slide the zipper heads into and it can only be opened by keying in the right numbers. The fixed point would make it difficult for the thief to zip it back. On a 3-digit lock TWBT has to try up to 1,000 number combinations before he/she could move the zipper heads in order to do the zipping-back trick, making it more time consuming to make your suitcase appeared untouched.
2. Use luggage strap to secure your suitcase.
TWBT has to cut the strap off before opening the zip = more time consuming = more risk of getting caught = good deterrent. In addition, a brightly coloured/uniquely patterned luggage strap could help you to identify your suitcase better, especially if yours is a generic suitcase that's also owned by a thousand other people. The strap could also help to prevent embarrassing situation like spilling the entire contents of your suitcase on the floor when it accidentally burst (because you have shoved in too many things in there... LOL...)
3. Wrap your entire suitcase in clingwrap plastic.
We've seen this wrapping service offered in some airports for a fee. I think the true intention is to prevent the suitcase from bursting. In this case, TWBT has to rip the plastic off before he/she could do the pen trick = very good deterrent.
That's all we can think of for now. What do you think?
Disclaimers: the above are just "helpful suggestions", so we do NOT guarantee that your suitcase will be totally safe from prying hands even after you follow the above to the dot. Just to make it totally clear, in the event of theft to the content of your suitcase, we are NOT liable (legally responsible) for any loss incurred. :)