Why gripes about C enums should be taken in context

[utzoo!decvax!wivax!linus!genradbo!mitccc!jfw]

I saw this message which mentioned something about lots of people still used
to V6 causing the # character to be on a line by itself at the top/

What is the meaning of a # character all by itself?  What meaning did it have
in V6 that it appears to have lost since?

John Woods
...mitccc!jfw