In doing this, we created updated dashboard cards that are used to request a charge or to be clear about giving permission for someone to unplug our car. This has worked out really well, allowing more people to take advantage of the chargers.
The card is used by marking with a paper clip your car's signal for full battery, and marking with another clip a time of day that is OK to unplug after.
The first card is for both LEAF and Volt owners.
The other two cards are Volt specific. This card is used to request a charge. It includes instructions for how to be sure that charging has started, and how to switch the car from delayed charge to immediate charge. And this card is used to give permission to unplug. It shows only the Volt's light signals, not the LEAF's.
I print these on card stock and keep a supply in the parking garage with the chargers. Hope you find them useful.