It didn't end well.
Democratic dissent is not disloyalty, it is a positive civic duty
I remember that incident.
So - The air traffic & operations staff should have been aware that the aircraft parked on its particular slot would not have been due out as it would have had a flight number, departure time & a crew would have signed the aircraft out. They should have become suspicious as soon as the first engine started up without any call for permission to do so let alone taxi out.
But things do happen!
If I remember rightly we used a security tape on the door if it was an unscheduled layover, a tech aircraft etc it was only ever for signs of interference
it did not however stop the gems boarded on a flight in Liberia being stolen in Banjul when we had a tech nightstop....it did of course warn that all had not been well overnight. Ooops
as an aside we were looking after the Queens Flight , Andover / 748 in Lusaka ... it was flying daily around Zambia and had a soldier guarding it overnight outside my office. Well when we came in in the morning all hell let loose as someone had written something on the leading edge de icer boot area ( I did not actually see it) and the RAF lads were not happy and thereafter nicknamed the mirror munchers ...? but I’m pretty sure they had locked the aircraft
Tell tale tapes were a late addition on the truckie fleet. it was a pain having to go round a stick them on all of the easy access panels.
On trips where Albert was carrying loads associated with 'nuclear sunshine' or something equally sensitive we carried a security detail of RAF Police.
They had the sh1tty end of the stick being left on the aircraft parked in a remote area overnight & often surrounded by a security cordon.