The idea is stupid, it's not going to stop spamming, say the limit is 30 posts, not many people do 30 posts per day. Someone who spams everyday will still spam, he wont even notice the limit because he does not post more than 30 posts a day. The only way to stop spam is to have a few mods or people searching for spammers everyday, ban sig campaigns like yobit or give them a warning to do something about their spammers.