Is there no chance of changing the board software so as to make everyone's first post(s) go only to a moderator, and require them to be marked "OK" before they are clear to post to the rest of the Forum?
The Yahoo groups have such a thing - the (much neglected) Lex Hermeticum group has that rule.
It just seems that nearly every new user who makes 1-3 posts is joining solely to have an account to post spam. The number of genuine newcomers is quite small...
[Captcha has been and had its day - spammers pay a pittance to 3rd-world humans to read and answer captcha questions.]
I just set the limit on the number of links in sigs to 3. If it keeps being a problem, I may disable links in sigs altogether, though I hate to do that since quite a few legitimate users have legitimate links in their sigs.
After much research, I think we've figured out how to require moderation of the first post of new users. Please let me know if you encounter any trouble with it.