Watch the attached video clip. Per PMB 2329:

New Keyboards Firmware
 
 
The enhanced physical keyboards interface with on-keyboard indication of SHIFT, SHIFT LOCK, FUNC, FUNC LOCK, CTRL and ALT keys for QWERTY, AZERTY and Numeric keyboards - requires new keyboard firmware.
 
The new firmware cutover production date was June 13, 2013. Previously produced keyboards require firmware upgrade. The firmware and the upgrade utility are posted on Support Center and the upgrade instructions were added to the updated Product Reference Guide 72-164686-01 Revision B.
Currently, without the enhanced feature, it is possible for an application to mask the screen preventing the user from seeing the status of these keys on the bottom of the screen. With the enhanced feature, the backlight of these keys will flash when pressed and flashed faster when pressed twice to lock (SHIFT LOCK and FUNC LOCK).
This is effective under warehouse lighting conditions where the backlight is clearly visible. Amnon Ish-Hurwitz