That manhole cover from Operation Plumbbob.
“YOU ARE HERE” map.
A giant ship that can transform into a giant robot maid, complete with a vacuum to suck planets’ air.
Sprinkle some water on the moon
A lone white lawn chair on the surface of Mars
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Dark matter, duh.
I’d suggest 35,000 low-earth-orbit satellites but Elon is already working on that.
A very small probe that emits an impossible to miss signal at random pretty long intervals and then adjusts its orbit to be very different. It would basically pretend to be various Aliens civilizations trying to contact us. Like every 45 days a new signal from a new part of the sky is picked up and then never repeats and if were just getting tons of messages at once. And since the probe is small and doesnt have a predictable orbit it would be very hard to figure out that its actually a probe and then find it.
Alternatively. A plane full of snakes.
A single protein molecule.
Something subtle enough to spark debate and controversy but not overplaying it like putting an entire living thing from Earth would be.
