> What is this, open crates or sacks of packages, in traincars locked with a small padlock?

Yes, pretty much. Although in many cases it’s not even a padlock, just a tamper-evident seal device with a serial number matching the paperwork for that container:

https://shipped.com/img-parts/server/php/files/containers/sh...

For huge cargo firms handling tens of thousands of containers daily, padlocks can be problematic operationally and quite expensive.