The Siberia 650 microphone only supports mute on/off illumination when using the USB sound card. When the microphone is muted, the mute LED light will turn on. Rotating the left inner ring back will unmute the microphone and the mute LED will turn off.
Plugging the headset directly into your computer or mobile device via the 3.5mm jack will not allow the microphone LED to illuminate if the USB soundcard is not plugged in.
GLHF!