I suggest using reCaptcha for the signups.
GJ on Akismet, although I'm not sure how well it will work against what seems to be very targeted spam, altho the same goes for reCaptcha, if it's manual spam, it won't be stopped by it.
GJ on Akismet, although I'm not sure how well it will work against what seems to be very targeted spam, altho the same goes for reCaptcha, if it's manual spam, it won't be stopped by it.