For reference: [edit] my post references the wrong Braccio. See Post #3.[/edit]
The shield contains three status LEDs:
Green LED (LED ON) signals that the shield is on
Another green LED (LED OK) signals that the shield is correctly powered
A red LED (LED ERR) signals that the shield is not correctly powered
That information is for the original TinkerKit Braccio. The Braccio++ is a different product. The documentation for the Braccio++'s control board is here: