There is an aircraft that I know of, it is a 747-200 N706BL. I know a tail number can be used to track the flight on flight aware, but today the company made a short flight, and used a different tracking number BTL101. How is that possible and what guidelines does FAA allow this?
After doing some research, I found that this is legal. I just learned about the three letter and three number destination. ICAO, if I remember right. 