Looks to me like the nation symbol is the element itself, and the bending symbol incorporates more of the bending lore, and swirls to indicatr bending. The moon and the ocean for water, a badger-mole's rear end for earth, etc...
I now want little tokens that come in one of those little velvet bags that have all those symbols on them. I would carry it around with me just so I could bust out some ATLA lore whenever I felt like it and leave a bunch of strangers confused. Autistic and loving it. ✌🏼✌🏼✌🏼