At least about 15 years ago I already used to get a reward for placing advertisement in my signature on some forums.
Most forums I know don't allow to earn money from your signature. It's meant for personal things, although it could include your own website.
What makes Bitcointalk unique, is the level of freedom we get. Of course, it also helps that the forum owns $40M. Most other forums rely on advertising, and advertising in signatures would compete with that. Bitcointalk doesn't have that problem.
So, apart from here in bitcointalk, has any other forum or website adopted the signature campaign system of advertisement?
I haven't seen it, and even if it existed, I'd expect it to pay
much less.
Does theymos have a patent for signature campaign such that no other forum can replicate what is happening here without his permission.
From what I've seen, theymos prefers freedom instead of restrictions.