We often ship internationally to the EU. In shipping there we put an EORI number that helps speed up the customs process.
Currently, we hand write this number on each label. That's 3 times per package. This number is displayed on the last line after the country.
City, Postal Code
I think you could generalize this field as memo field for someone to put Attention: Shipping Department we would simply put EORI: 2389455758937