Dont know how USPS tracks orders, but if it has a bar code or something similar on it and they scan it when it moves into the country?

The signature / delivery thing; it helps make sure the package gets there, no sig no delivery, if you can afford it you could probably get almost any thing sent like that.

What exactly happens will depend on exactly how USPS delivers the package in each individual place, I would think they use a local delivery service. Either that or some poor posty in the US just got a large stack of OoTS books for every from the UK to the Netherlands and back again.

Just think of all the air miles.