Nothing, known spammers just get empty page. You can add a message if you like by editing the end of join_process_form.php
if($spambot == true) {
echo 'Get Lost, Spammer.';
exit;
}
That would be better suited for a custom project, I don't think that would be useful for many (any?) other users, its hard enough to get followers to 1 twitter account nevermind splitting your twitter efforts into an account for each category.