It is illegal in Oregon to "feed, harass or capture" wildlife unless it is hunting/trapping season for the specific species. If the people knew what they were doing, they would have known this. They would have known not to put a collar onto a fawn that it would quickly outgrow and then become strangled by if it ever ran away. They would have known that a fawn that still has spots on it has not yet been weaned off of its mothers milk. And they would have known that the best thing to do would be to leave the fawn where they found it without touching it. If I were wrong about any of these facts...which I am not...the Department of Fish and Wildlife would have told be that when I called them instead of getting the State Police involved.
Maybe the mother was killed by a car. You can bottle feed a fawn just like a calf. After raising it in captivity though it shouldn't be released as they have no fear of humans, wouldn't be fair to the animal during hunting season. I wouldn't call it common, but some farmers around here raise them. They're usually found while cutting hay as they use the tall hay as camouflage, if mom was alive she would be close by and visible.