matching subjects with words in []

i'm on a couple of mailing lists which ask that people start subject
lines with constructs like [MAC] or [ADMIN] to make it easy to sort
out what you're not interested in.  but how do i match on these with
procmail?  the grep manpage led me to believe that if the brackets
were escaped with backslashes, they'd be treated as regular
characters, so i thought \[MAC\] would match [MAC], but that doesn't
see to be the case.

thanks for any suggestions.