The Right Note

Through the streets of an Irish city I was striding with a friend. We observed a car backing into a small space on the side of the street. Behind the car was a parked motorcycle; the driver did not see the obstruction, and down went the motorcycle with a clatter.
The driver got out of the car and examined the scene. It appeared that nothing was broken- so far as one could tell, anyhow, given that no dents were visible and no fragments of metal had detached from the machine.
Still, it had been a mighty collision, and one could not surmise what mechanical elements had been affected. My friend and I stood nearby, and we wondered what would happen.
The driver, it seemed, was not particularly concerned, for she set the motorcycle upright, returned to her car, locked the doors, and strolled on down the street as though nothing extraordinary had taken place.
My friend and I were having none of that nonsense, that rude disregard for the property of others. My friend was a visitor. It was my country, and I supposed I ought to know the protocol for such curious circumstances.
We reached a solution together.
We scribbled a little note and slipped it inside the fellow's helmet. The message stated that, should he find any trouble with the vehicle upon his return, such and such was the licence plate number-and the colour, and the model number- of the errant car that had struck his motorcycle.
That was years ago but I wonder to this day what crossed his mind when he went to put the helmet on and got a bit of notepaper stuck in his ear; and I wonder whether he needed to use it; and what it felt like for the thoughtless driver to have the covert deed mysteriously return to haunt her.