There are a lot of cases where innocent people would be penalized under the proposed system. People who don't post that often, those who go on a break from the forum, people who post in sections where merit sources are still thin, etc would all have a much higher risk of unfairly having their signatures removed. The last thing I'd like to see is decent occasional posters begging for merit or posting when they don't want to just so they can keep their signature.

I think the better option is to just let the account farmers continue to get frustrated, and the moderators will find them eventually.