I think if signature campaigns were disallowed then there would likely only be those that are truly interested about discussing Bitcoin, and a few veterans users here.
This is justifiable as there are a lot of users who are willing to stay on the forum as long as they can make something out of it. Signature campaign and bounty campaign are one of the reasons why many users are using this forum and therefore the user base of the forum is increasing.
We know most forum users have different goals to join this forum, there are only some users who are really interested in getting to know bitcoin technically while others are bounty hunters, traders, gamblers and spammers and other. If bounties and signature campaign are removed or banned, the user base will decline rapidly. I am very sure of that.