Asus ESC500 G2 - Manual (Page 50)

Chapter 3: Motherboard information 3-8
3. EPU LED
The EPU LED lights up when the EPU switch is turned to Enable.
4. Standby power LED
The motherboard comes with a standby power LED that lights 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 LED.