So far I have figured they are ON in Park mode (P button pressed) OR if you have the lights in PARK mode from settings. I am not sure if that means the tail parking lights also turn on when driving, I suppose not but can't confirm without having someone else check for me whole I drive. If I go by the dashboard X replica, those tail parking lights must be off.
As for AUTO setting, only the saggy-eyeliner DRL lights turn on, no fangs. This is also confirmed by observing the X in summon autopark mode.
I would drive in PARK mode all the time if that's what it takes to show my X fangs, except at night when PARK mode means no headlights... damn you Tesla!!!