Asus Z9NR-D12 - Manual (Page 40)

2-20 Chapter 2: Hardware information
1. DIMM Error LED (ERR_DIMM)
The DIMM Error LEDs light up to indicate an error in its nearby DIMM.
2.6 Onboard LEDs
2. Baseboard Management Controller LED (BMC_LED1)
The BMC LED works with the ASUS ASMB6 management device and indicates
its initiation status. When the PSU is plugged and the system is OFF, ASUS
ASMB6 management device starts system initiation for about one (1) minute.
The BMC LED blinks after system initiation finishes.