In new cars you often see these white marks on the front ceiling of the car. These marks are made by a monk when he blesses the car.
When a person buys a new car, they take it to the local temple for the monk to be bless it. They do this because they believe it protects the car from calamity. The monk chants over the car and puts the marks to invite the spirits to bless the car.
The more I observe the phenomenon of traditional religion in this culture as it is in many cultures, I see how and why traditional religion is held onto, even when Thais are Buddhist. Traditional religion deals with the ever present questions of the here and now: how to gain success, protect myself from evil, explain death, and so on. Buddhism deals with large overarching questions of morality and what happens when we die, but doesn’t directly deal with the practical day-to-day life. The practices of local religions remain in order to deal with these day-to-day happenings of life.