Pioneer is demonstrating a very nice looking transparent OLED automotive brake system. The idea is to embed this unit in the vehicle's rear window - so it is transparent and allows for a greater field of view, but when you press the brakes it emits a bright red light:

The idea of embedding an OLED in the rear window is not new, but this is a nice implementation by Pioneer.

Pioneer transparent OLED automotive break module prototype

Pioneer, together with Mitsubishi Chemical Corporation have developed a color-tunable and dimmable OLED lighting panel produced using Mitsubishi's wet-coating process, and the two companies say that this new panel will be mass produced in early 2016.

Kyulux - Hyperfluoresence OLED emittersKyulux - Hyperfluoresence OLED emitters