i thought that the Red Diamond represented the Amulet Of Kings :shrug:
It represents Pelinal, who was in the shape of a gaping wound - the wound in Shezzar's chest, where his Heart used to be.
Also note the difference between the symbol for Skyrim and the Imperial Dragon symbols in earlier games.
Don't notice a difference? The diamond symbol is broken. That's because the covenant was shattered when the Amulet of Kings was destroyed. The Amulet was gifted to Alessia in some stories by Akatosh and others by Shezzar.