I have no idea about the checkmark. Amiga Inc and Hyperion pushed the Boingball so aggressively I always assumed the checkmark was owned by no-one and so generic as to be not actually trade-markable.

It isn't very Amiga specific either. The 3.1 disks had a rainbow (and later standalone ones had a falling block check pattern). The 2.1 and 3.0 disks had a funny colour paint smear in a square thing. AmigaOS 1.3 didn't have anything AFAIR, just the Commodore chicken lips. It was only older 2.04 disks that had the rainbow checkmark, as far as I know - although it apparently varied between country, Amiga model, and source.

Who owned any of that? No idea.