The main man at Irrational (who is apparently also a CAG) sent me an email to let me know about this offer, only available if your order from Irrational's store. First 500 pre-orders get the autographed artwork.
https://www.freedomfans.com/store/index.php?main_page=product_info&products_id=173
https://www.freedomfans.com/store/index.php?main_page=product_info&products_id=173