Thank you all for your feedback!
[..] Why would I choose solar shield over this? [..]
Because it reduces the damage by 1 (as dragonsdemesne mentioned). Especially against low atk creatures, this helps a lot -> Adrened units are much less dangerous with the Solar Buckler. With the Insignia, you benefit even big time but take the full blows.
[..] Still, it's enough stronger than solar shield that I think a change should be made in the cost and/or effect. I suppose you could make it last only a certain number of turns, wings/dimshield style, as well.
I can't deny that. Same duration as Dimensional Shield seems appropriate to me. Thanks for the hint.
There seems to be room on the card still... maybe add an interaction with spell damage as well to set it apart?
Good idea. The background of the castigation thing leads me to x1,5 damage for spells because it's the *cowardly, inglorious way of fighting*. But there is no space in the card text field for that...how to solve it?