This will bar them from getting paid to post and not have any negative impact on anyone making even the tiniest contribution to the forum. Nobody loses their rank and even if someone is away from the forum for a while they can quickly get their signature back.
Interesting idea!
But we'll need additional features to make this work, you'll need some indicator for campaign managers (or anyone) to know that a forum member's signature is being hidden due to merit so the Campaign Manager will know not to pay the person. There would also likely need to be tracking to the exact post or date and time that the forum member's signature became deactivated (and reactivated) so Campaign Managers know what to pay when a deactivation comes mid-campaign cycle.
This would probably cause a lot of campaign turnover, which could be worse for the forum. You end up getting every "newbie" or Member rank getting a 2 month tryout on a campaign whether they have good post quality or not!