If you are 100% sure that it is stray/wild, kill it. If it is possibly a pet that just wandered away, let it wander back. I've had it happen both ways.

If it appears to be a pure bread, groomed dog that just doesn't happen to be wearing a collar, I'd bet it belongs to somebody. Pets are off limits.

I've had hunting dogs come through running coyotes before. They'll roam the countryside chasing coyotes, scaring the deer to high heck basically ruining the hunt, all while the owner sits in his truck and waits. Only then do I get a little ruthless...