RRG, page 16:
RRG, page 16:
Shield cards are discared rather than played and then go into the discard pile (never entering play) so I'm inclined to say you could use a second copy for the shield effect.
Now my bet is FF will make sure the situation doesn't crop up.
Shield cards do not enter play and therefore are not affected by the limit on Unique cards. They are discarded from your hand and go to your discard pile. Your hand and discard pile are both out of play.
So far, the only unique card with Shield icons is Cato Sicarius' signature attachment, so you cannot have two of them in your deck. But if any non-signature unique cards with Shield icons come up, refer to Toqtamish's answer.