Signed up to another forum the other week and had to give enough details to open a bank account. Yes I know people will lie about it. But then it took almost a week to get my rejection letter. How about rejecting every signup the first time it is submitted saying there were some signup details missing and suggesting they resign if they wish and to fill in the form fully. If people are really serious they will try again, as I did, and get approved. This may at least put a lot of people off who are just spamming. Going through the signups probably wont take as long as chasing the junk posts.
Just my 2c.