When someone is leaving on a journey, a customary tradition is to throw water on the back of the car as it is leaving or behind the car as it leaves. The reason behind this is to wish for your travels to move as smoothly as water flows. When the person is leaving the way you say bye is to say ?yi yolculuklar which directly translates to Good Journey/Travels. The meaning though is Have a good journey/trip/travel
Although Robert is from America, he has spent a lot of time in Turkey because most of his family resides there. He does not know the specific time he learned traditions such as this one, he generally acquired knowledge of them as he grew up and spent more time in Turkey. People across Turkey still practice this tradition on a regular basis.
Iyi yolculuklar is a very universal, polite phrase. As far as I am aware, most people wish others a good trip when they are leaving on a journey. The odd part to me was throwing water on the back of the car. When I talked to Robert further he did not really know the significance of this, it was something they just do. I assume the water had some significance at some point. My speculation would be that it was some sort of sign of good luck that you were throwing towards them as they headed off on their journey. It could also represent something bad, since you are throwing the water behind the car, it could be symbolic of leaving the bad behind.
Traditions like this are one way a showing an identity. If you did this some where other than Turkey, people would probably have no idea of what you were doing. Even people who study the Turkey may not be aware of this tradition because they have not been immersed in the culture. This is becoming less of a problem though with the internet. People can find traditions such as these either described or videoed on the internet, so they can maintain this knowledge without ever having to experience the Turkish culture first hand.