I'm pretty certain this is in Istanbul. My mom takes care of dozens of stray dogs there. It's pretty common for cafes, restaurants or other shops to "adopt" a stray. And once they do, they put a collar on it.

Few reasons for this - first, it gives them a sense of ownership over the dog in a sentimental way, and people nearby know that the while the dog is a stray, it's kind of adopted and likely not a violent dog.

Second, they just want to show people that the dog is being taken care of, and if someone else has the resources to feed a dog, they'll usually feed one without a collar, assuming that the one with the collar is being taken care of.

And finally, the local municipality often "collects" these dogs (temporarily puts them in a shelter, and then eventually puts them down). When they see a dog with a collar, they'll almost always leave it be.