In number plaques for mailboxes there is always a margin of creativity. There is no hard and fast rule for the shape of a mailbox . A mailbox a can literally be any shape and size. Depending upon the requirement you can place the mailbox at a place where it can be seen so the visitors. You would obviously like your mailbox be unique, and at the same time it should have some sort of distinctiveness as well. You can write your house number or you can also print the number on your number plaques for mailboxes if it is required.