Copyright transfers may have to be written, but if it is truly work made for hire then there is no copyright to transfer. Typically an employer would state both that it is work for hire and additionally stipulate that any copyright is transferred, but this is just covering of asses in case a court finds it’s not actually work for hire. Spiegelman’s argument is that Copper would have assumed that this was a work-for-hire arrangement, and that he thus never had copyright, in which case there is no copyright to assign or transfer.
