It's easy to provide proof of capture. 2266 kilo one-cubic-meter cubes of carbon, by the billions. Preferably stacked into interesting and eye-pleasing shapes.
Casually building pyramids out of the ~57 cubic kilometers of carbon blocks would be pretty neat. three 4 kilometer tall square based pyramids would do it.
They would also be the largest structures ever built by humanity by an order of magnitude.
