Sorry for my lack of knowledge about this, but are "ad mailmen" a specific thing in the Netherlands? In the U.S., junk ads just come in the regular mail.
If it is like in France (we have the same regulations) then you have two kind of junk mail :the one addressed to you (because they have your mail status, supposedly because you have it to them and agreed to get mail spam) and anonymous one (from supermarkets for instance, with their promotions or sales) which are delivered by someone payed by them. The stickers work for the latter (which is maybe 70% of the volume)