I'm thinking user groups...maybe something like this:
0 posts: Can't haz sig/URL/etc. Can't post visitor messages/etc. Basically, can only read stuff and post forum messages.
1-10 posts: Can't disable sig in posts (so we will see their post).
11+ posts: Regular user.
Just enough so we get a chance to see them without having to check every damned vBulletin feature. I don't fucking know and I don't feel like figuring it out right now.