AAEON EMB-BT1 - Manual (Page 19)

2-11 Chapter 2: Motherboard information
EMB-BT1 Onboard LEDs
SB_PWR1
ON
Standby Power Powered Off
OFF
SB_PWR2
ON
Main Power Main Power Off
OFF
1. Standby Power LED
The motherboard comes with standby power LEDs that light up to indicate
that the system is ON, in sleep mode, or in soft-off mode. This is a reminder
that you should shut down the system and unplug the power cable before
removing or plugging in any motherboard component. The illustration below
shows the location of the onboard LEDs.
2.7 Onboard LEDs