Many years ago, a company pitched me an intriguing product to review: a display you mount in the rear window of your car, which you can use to send customized messages to drivers behind you. With the tap of a button near your dashboard, the display would light up with a scrolling message of whatever it was you wanted to tell other drivers--a great way to get pulled over by a cop, if not outright killed by some already-angry tailgater. The Silicon Valley startup Drive.ai The theory is that digital signs would make self-driving vehicles a bit safer, since they don't really have a great way of letting pedestrians know their intentions beyond simple turn signals. The sign would be able to indicate various statuses about the vehicle to those near it, including when it might be safe to lane-split (because the self-driving car has noticed you and promises to not merge into the next lane and smoosh you).