DdBob
Dogue in teh desert
I think when they first came out they were worn on the rear when people used them in their OG intent which was short hikes and people still wear the big behemouth ones for dayhikes on the back (some search and rescue, etc) but back packers and townsfolk wear em in front (the most logical quite frankly for access and security) and hipsters wear em around the chest for some reasonIt's called a bumbag in the UK.
But I've never seen people anywhere wear them with the bag in the back. Definitely doesn't seem like a good arrangement if you're worried about pickpockets.