Hi there! Thanks for writing in!
In short, there is no symbol for the Sun that is accepted and used by all Native American Tribes. There are 574 federally recognized tribes with their own religions, languages, art, and customs.
Every tribe has different associations with the universe and animals, what may mean one thing to me could be something completely different to you based on our tribes.
For example, owls are considered to be good omens in my Tribe (Zuni), but are considered to be bad luck in other Tribes, like with Navajo.
In regard to the sun being represented by a common symbol, there are some similarities between Tribal designs, but again there will be different stories, beliefs, and associations from each Tribe.
Hope this helps and best of luck!