Ear Tags for Dogs

I just got back from Istanbul, I was there for the F1 race this past wekend. While I was there I noticed some of the dogs had ear tags, similar to what you see used on livestock. There was a wide variety of dogs running around the city. There were skiny unkept stray dogs, the mixed/native dogs that we couldn't tell if they were owned or not (these were the ones with the ear tags), and there were a few purebreds (golden & boxer) that were well kept with collars. We couldn't tell if the dogs with the ear tags were owned by anyone sepcificaly or just accepted by the community. They weren't skinny and mangey like the stray dogs. And they were allowed to enter and sleep at the cafes/resturants, whereas the strays were shooed away and treated like pests. Does anyone know what the ear tag signifies? Does it mean those dogs have owners or are special for some reason? I know we have members from all around the world here, so hoepfully someone can fill me in.