Callsign, registration and hex: what is the difference?
A callsign names a flight, a registration names a particular aircraft, and a hex code is the aircraft’s unique radio address.
Callsign
The name used on the radio for a flight, for example BAW123. It usually starts with the airline’s three-letter code. It can change from one flight to the next, even with the same aircraft.
Registration
The aircraft’s own identity, like a car’s number plate, painted on the fuselage: G-EZBK, N12345, D-AIMA. The first letters show the country it is registered in. The same aircraft keeps it for years, whichever airline flies it.
Hex code (ICAO 24-bit address)
A unique code built into the aircraft’s transponder and shown as six letters and numbers. It is how tracking sites match a signal to an aircraft, even when the callsign or registration is missing.
Why it matters for spotting
The Sticker Book uses the registration, because that is what makes a sticker belong to one specific aircraft.
Watch for it
On a live stream, note the registration on the tail or fuselage and compare it with the one in the list.