USPS does not own the box, but they have exclusive right to it, as well as the placement specs to insure proper USPS delivery. When the USPS writes the number on the box they are doing everyone a favor. Many times you will even see color coded stickers placed on the box by the newspaper guys to show what paper to throw or place in the open slot intended for papers. If the Fedex or UPS guy comes along and helps the number situation, so be it. Why should anyone have to guess including first responder's or even the IRS. If the IRS has to come to your door, they WILL find your door regardless of the numbers on your mailbox.