I was on another forum for earning money and there were also some signature campaigns but the earning was lower that what from this forum. But the best source of earning is to start your own site or start any online service.
They do usually payout small amounts of bitcoin compared on this one (bitcointalk) because it depends on the traffic on a particular site and if a newly built bitcoin forum would be established then it would really strive to get new traffic out of the site since most bitcoin or new users would definitely always go on the reputable ones than on newly built website.