So, in the previous image, Atom was wielding a sword and a shield. This is a close up of what his shield would normally look like. It's slightly based off of an Ancient Shield from BotW, so it is capable of reflecting energy based attacks. However, it's emblemed with Atom's Shifter Symbol. Not to get too technical, it's just a representation of his main Realities. Might end up adding a DNA Helix or some wings somewhere to incorporate the Mega Dragon into it in some way at some point, though.