金剛經纂要刊定記 3.76

3.76

從佛下。指經。是無下。釋名義。此即相之無相，非一向之無相，略見行玄為順本宗，故標無相也。

"From the Buddha..." points to the sūtra. "This is signless..." explains the name and meaning. This is the signlessness of signs, not an exclusive, absolute signlessness. Glimpsing the abstruse nature of practice to accord with the fundamental tenet, it therefore designates it as signless.