Why does Rafale have RB 001 written on it?

India had entered into an inter-governmental agreement with France and Dassault, the French aviation major, to acquire 36 Rafale fighter jets in flyaway condition at a cost of Rs 59,000 crore. A Defence Ministry official here said the meeting between Macron and Rajnath at the Elysee Palace in Paris on Tuesday lasted for more than half-an-hour. The Rafale aircraft will be handed over to Singh at the Bordeaux-Merignac Air Base