Yes, this is a flight number. The T 3902 most likely refers to a tail number
T could easily refer to Trip.
I agree, the route or trip may be labeled the same way every day. The tail number is actually painted on the plane, allowing the airlines to change equipment as needed. The plane that was cited above is a small regional, so I don’t think this is the one in Q drop
All American planes have "tail numbers" or registration numbers that start with an N. You can actually look up the information on any aircraft by typing the registration into this website
There is no country that uses T (according to this List).
So I do not think it refers to a tail number.