Here is a smartphone controlled LED car sign that lets you send messages to other drivers on the road. Ototok is pretty easy to use. Simply install the sign on the back of your car, download the app for iOS and Android, and pair your phone to the Ototok. You will be able to use your smartphone or a dedicated RF remote to interact with this car sign.
The device is powered through a 12V power supply. It supports multiple languages and emojis. Like what you see? You can find this project on Indiegogo.[Source]