Yeah, I thought so, because a few weeks ago I was browsing through some threads from at least 2011 and stumbled across a person offering to rent out his signature space, and the comments on it made it quite clear that this was not yet a thing.  I don't know how I randomly came across that thread, but it was fascinating.

I'm really surprised other forums haven't caught on to this yet--it'd probably wreck any forum that did it in terms of post quality, but I don't think it's common knowledge that bitcointalk is a signature campaign hub.