>>11797180 (lb)

Corn ink

Ethanol itself doesn't necessarily have a traceable signature, but some of the other components (corn oil, saccharides) that can be used to manufacture ink do.

Ethanol is added to keep the ink in a slightly more liquid state, which then evaporates off to "dry".

The corn itself could easily be tagged, radioisotopes added to the water (plants need water) that would then be incorporated into the plants and eventually the ink.

Ink from other sources would not have the same radioactive signature.