How to know if the System Management Controller (SMC) has been reset?
Actually, as per my experience if you are going to do the SMC reset and your not fully charged battery Macintosh machine is charging, the charging indicator will be the reset indicator as below.

When battery is not fully charged:


Charging indicator is orange light when machine powered off.
Keep pressing Shift + Option + Control + Power for 10 seconds and indicator is still orange.
Indicator turns to green when release all keystrokes and keeps almost 1 second.
Light turns to orange then.