From the Rumor Mill, Scottish office:
Air traffic controllers receive details of the arrival of a plane with a US special call sign weeks in advance but are not told exactly which plane when the booking is made. The source at Prestwick airport, who asked to remain anonymous, said: “There is a booking for an American military version of the Boeing 757 on January 19, the day before the inauguration. That’s one that’s normally used by the Vice-President but often used by the First Lady. Presidential flights tend to get booked far in advance, because of the work that has to be done around it.”
https://www.sundaypost.com/fp/donald-trump-could-be-planning-turnberry-trip-as-scots-airport-told-to-expect-a-high-flyer-the-day-before-joe-bidens-inauguration/