>>58158200the meaning behind the sigil is explained in the leaks and explained in further detail in pmyth5.2 AUSU.
The fact that it appears not just in HG/SS to explain the origin of pokemon eggs from Arceus but again to show Arceus' earthly domain confirms the divine order of the pokemon world.
Other legendaries are also explained in pmyth5.2 AUSU as the tree of life portion explains Xernas(Tree of life branches), yveltal (Tree of life roots).
Unova, Alola, and Galar legendaries are more regional than being in the godly order. Hell Eternatus and the ultra beasts are from outer space.