I sent my signup to the list using the *old-fashioned* way: I sent an email to fedora-infrastructure-list-request@redhat.com (and to fedora-documentation-list-request@redhat.com) with "subscribe" in the subject and mail with a standard signature (marked by dash-dash-space on a line).
Both replied twice (for whatever reason!).
I also seem to have sent off an HTML mail for my intro! Ack! I expected it to ask (at which point I'd use text only) but natch....
infrastructure@lists.fedoraproject.org