i mentioned elsewhere but if you had a large octocopter (think like 8' across) you could fashion lights to it to imitate other aircraft, like nose and tail and wing markers. My DJI has a front and rear light, the rear one blinks two colors so you know which side is which, my older DJI clone had lights on all four rotors, different colors between front and back (green and red? or am i confusing boat markers, haha).

If i wanted to freak a bunch of people out i'd start my design like this, at least. Some aircraft can fly really slow (biplanes, for instance), but the videos i saw of ostensibly these aircraft they were moving too slow to be actual fixed wing aircraft of the shape the were implied to be by the lights. But who knows if the videos were doctored (cropping would fool my brain about relative speeds), or even of the aircraft we're talking about? I didn't save them so i got no idea, sadly.

Clearly, my spy craft isn't a spy craft. Look, it has lights on it for Pete's sake.

Plausible deniability

It'd be more clever to have lights and leave them unilluminated. If caught they can still claim what you're claiming, adding "You just didn't see them!".

Well, let's say they are spy craft - seems the "it's not real" narrative is working, no?

My favorite part is the part when they say "Aha! It's camoflauge! It LOOKS like an aeroplane but in fact it's a disguise!". I mean, what's next, a helicopter is chasing a drone and they say "Aha! The alien craft has disguised itself as one of our helicopters chasing one of our drones, who would suspect that!"

Anyway the non-alien conspiracy theories are along the lines of radiation sniffers for a suitcase nuke, drone tests for material transport between bases & offshore navy ships, red team vs blue team drone tests.