we bring a small roll of packing shrink wrap.
we wrap our luggage with it before we leave home, and before we get off the ship. It also helps when we have to stack pieces for Debarkation.
we get everything from strange looks to, people pointing saying its a great idea..
as as far as leaving your luggage unlocked , never. We lock it, and wrap it. If they want to get in to see something, they call us down. The airline thieves have never opened our bags either.