I assume it should tell them that the retailer has availed of the EU's import one stop shop and has therefore already paid the VAT to one of the member states. But I honestly don't know if it's there for the carrier or customs or anybody. In different countries, the carrier is responsible for determining and collecting the VAT and in others (like here in Germany) there are customs officials working in the mails centres and they determine the VAT and duties due and put a sticker on the parcels. It's still a pretty new facility. I guess some officials are still not looking for it, though you'd imagine if it was important it would be much more visible?