Holograms are caused by polishing with a rotary, generally "imperfect" polishing where it doesn't leave a perfectly smooth surface. One of the biggest challenges with the rotary is *not* inducing holograms. They are just another form of "marring" (in this case, near-microscopic, circular scratches) and are removed by polishing with an abrasive.
They look like rainbow-colored swirls and are generally only visible in bright sunlight.
I remove them with a PC/Cyclo and a mildly abrasive polish.
Try a different search; holograms have been discussed at great length.