The TSA can be bloody-minded over this issue!
We have (sorry, had) a Samsonite Oyster hard case with a built-in combination lock. As it tended to open involuntarily if left unlocked, I spun the tumblers and sellotaped a large note to it "THE COMBINATION IS 0000 IF YOU NEED ACCESS". (Yes - I had even reset the combination to its factory setting!!!!)
On arrival at Houston, the ignorant ba5tards at the TSA (I know it was them cos they kindly left a letter on top of my clothes) had used a saw to cut out the lock!!! Obviously whoever they employed couldn't read English (or couldn't read!)
Don't Lock Your Case!!!