they just have to setup the forum software so that the first post of a newly registered member has to be approved by a mod.
I think it would work better if links in posts could be disabled for new accounts, until a reasonable time and post count limit, and possibly post frequency limits. That would be more elaborate to set up than enabling moderator approval, though.
Check if there is a mod for UBB forums that does that. I use the SMF forums and have been using a couple of mods that...
1. Prevent any new members from posting links (actually, it simply garbles the links so that they are not clickable) until the user has posted 25 messages, and
2. Use a mod that checks new member registrations against the "stop forum spam" database and anybody that is in the SFS database gets put into a manual moderation queue where an admin has to manually activate the account, (which never happens when they are in the Stop Forum Spam database.
I seem to remember that there were similar if not the same types of mods for the UBB forum software a while back somebody told me.
So far on one of my sites, the SFS database system has stopped over 56,000 spammers from finishing their registration on one of my forums.