In wisconsin i know that a vehicle without a trunk is not technically considered a locked container when your weapon must be SECURED due to windows being an extreme weak point. Much like "locking" your house with only a screen door. While technically this does not help you with your question per-say, it may give insight. My vehicle does not have a trunk so i use a fire safe. As far as leaving it in your vehicle because of a "target this business" sign, it would be sufficient.