金剛經纂要刊定記 3.93

3.93

智相者。經從「須菩提！於意云何？如來得阿耨菩提耶？乃至一切賢聖皆以無為法而有差別。」則以無相無為法為智相也。故《起信》云：「以智相無可見故。」

Regarding "the mark of knowledge": the sūtra goes from "Subhūti, what do you think? Did the Tathāgata attain anuttarasamyaksambodhi?..." up to "...all worthies and nobles are distinguished by means of asaṃskṛta phenomena." Thus it takes signless, asaṃskṛta phenomena as the mark of knowledge. Therefore the Awakening of Faith says: "Because the mark of knowledge has nothing that can be seen."