As clearly stated, on the registration form:
Joining the History Teachers' Discussion Forum
When you register on this forum, please use your full name or combination of firstname and initial. For example, Andrew Field or Andrew F. The aim is to continue to build a friendly community but also to establish people as individuals.
When you register your account, each account is manually approved by the site team. This means that your account isn't instantly available. If you join with a sensible name that will allow us to approve your account much more rapidly. We have had to introduce this measure because of so many spam registrations.
Thus if you register with 'fuddlydudley' or 'MylieMystery' (not that anyone did really ) it isn't going to get into the forum. We aren't doing this to cause trouble, but rather try to keep this forum running as effectively as possible. We've even had spammers follow the rules to try to get access!