We had a roomba mounted print head before.

Yes. It prints similar to an inkjet printer, but the inks are UV-curable. UV inks don’t need a special medium like coated inkjet paper, they stick to any surface. You can also layer multiple coats on top of each other to create reliefs (like resin printing, but with colours)

The technology could also be used to track the origins of illicit goods.

Does that mean ghost guns? That was my first thought when I heard of this tech.