They wouldn't know what is in the package so it wouldn't apply. I know any postal carriers I've had in the past, and others I shipped to, they will leave the package unless it had signature required (and even then 50/50 if they leave those too with no one around, as several would squibble something on the signature line).
If the package is left on a shaded porch or similar you should not have any problems, should be better than sitting in their truck too. Thankfully I never had any problems with my packages getting stolen, knock on wood, hopefully your area is the same; however, if your really worried call your local post office, give them the tracking number, and have them hold the package for you to pick-up. I've done it before and my post office has always been helpful.
