I’d bet this is someone’s “pet” deer that they don’t want shot and are trying to signal that. I’ve heard of people putting reflective collars and things like that on deer that they’ve kept as pets, to try to deter hunters from shooting them.
If that’s what it is then I totally get the impulse to help a wild animal yourself, but the average person VASTLY overestimates their knowledge of what wildlife needs to be healthy. Always contact a wildlife rehabber if you find wildlife in distress!
And then there's the dude I ran into at a bonfire a couple months ago talking about how he got a deer to trust him enough to come on his property and let him hand feed it and the instant deer season starts he was going to shoot it.