As they say, necessity can be the mother of invention. From the Associated Press via the Silicon Valley Business Journal:
When the vehicle is moving the license plate would look like the ones we’re used to now, but when the vehicle stops for more than four seconds a digital ad or other message would flash. The license plate number would always be visible.
Traffic information and Amber Alerts — notifications of missing children — could also be broadcast through the electronic licenses.
SB1453 would let the Department of Motor Vehicles explore the issue with companies that make the devices, and with the California Highway Patrol.
The bill passed through the Senate in May and is set to go before the Assembly Transportation Committee.