After one Midsummer some years ago, one of the rangers found a bunch of garbage laying around after some careless people's celebration. Among the beer cans, bags, leftovers and other litter, he found someone's name and number; I'm pretty sure one of them had literally left their business card. He proceeded to gather all of the trash in a garbage bag, looked the guy up, drove into Stockholm (some 40 km), rang the fool's door and handed over the trash while saying something like "Hey, I think you forgot some of your belongings!"
Edit: just found out from the Archipelago Foundation's Instagram that today is the international clean the coasts day!