Many sites have attempt to copy btctalk and even pay their visitors to post there but no one succeed. They are still a plain forum with no signature campaign in the line.
This is the oldest forum and paying their users regularly from signature campaign since its inception and it will continue to pay even in future but we cannot have same feeling for other forum as they may pay till they are now but in long term they may disappear or stop paying their users.
Recently you may notice the Reddit forum campaign ann also in the services section. Using different forum not for the signature campaign. It should most used by the people who are all been in this forum. Apart from signature campaign there are many reliable business and projects available in the forum itself, utilize of it.