There are possibly many different ways that you can decorate a modern mailbox. You might even be ale to find a home decorator who can offer suggestions. Just make sure that anything you choose does not conflict with your homeowners’ association, if you have one in your neighborhood. The last thing you want to do is cause a ruckus over your mailbox choice. This is something minute and not worth stirring up trouble for. If there are no restrictions, you are free to decorate your mailbox, within reason. Of course, you want to make sure that any type of design you choose is secure and approved for use by the US Postal Service.