I think there was a time when the forum never had signature campaigns and people were still actively involved.
I rely don't know what the forum will look like because I haven't ever thought of that.
On the contrary,  I think signature campaigns are one of the reasons people are making positive impacts on the forum because they have to work really hard to join a campaign and most times, your post quality and other factors are put into consideration  before accepting  one in a signature campaign, hence, one must have strived so hard to be in a signature campaign and without signature campaigns,  I think the forum might be more of a social media than a forum.