Can add Secretary Blinken to the list of no/empty callsigns'''
This is 100% a pilot decision to not input a callsign as ADS-B is only getting the data via the transponder and since there is no callsign input it displays it as it's tail # on the AC icon -in this case '99-0003' because it has to show something. Blinken has used this AC in the past-most recently a trip to Panama with DHS Mayorkas
99-0003 USAF C-32A departed JBA to the ne-Blinken no callsign as this should be SAMXXX.
This is Sec. of State Blinken heading to Berlin for NATO Foreign Ministers and then to Paris, joined by United States Trade Representative Katherine Tai and Secretary of Commerce Secretary Gina Raimondo, to attend the second ministerial meeting of the U.S.-E.U. Trade and Technology Council (TTC).
Secretary Blinkenโs Travel to Germany and France
https://www.state.gov/secretary-blinkens-travel-to-germany-and-france/