It is the stacking lights.
Off (no light) - Stacking mode is enabled and the switch is a stack member operating in slave mode, or the switch is operating in standalone mode.
Blinking green - Device is initializing Steady green Stacking mode is enabled and the switch is the stack master.
Steady amber - Stacking mode is initializing and the switch is the standby controller .
Blinking amber - Stacking mode is initializing and the switch is in stacking master arbitration/selection state.