If anyone is really concerned about the legalities of these things,
then there should be no 'comp.unix.xxx' groups. They should all
Use of Unix as a noun is an encroachment on AT&T's trademark, to which
they are legally obliged to object in order to retain their trademark.
(Trademarks can only be adjectives. If a trademark becomes a noun, it
becomes the common name for something, rather than a word which distinguishes
a particular variety from the general case.)
Look around in the manuals--at least as far as the lawyers have read, it
will always be written as the Unix operating system.