1. Did it improve your SEO?
2. If yes, then in what time frame?
3. How much influence it had on long term SEO ranks?
4. What happened when you stopped signature campaign?
5. Did your positions went down or did you still keep it?
Backlinks from the forums are really helpful. I had small crypto blog which I used in my signature, I used 4 blog pages on my signature and after few weeks I started getting views from google
I am not sure about other search engine but I started getting more views from Bing search engine than Google.
According to my experience below are answers.
1. yes it affects.
2. 3 to 6 weeks (it depends on the keyword you uses to add)
4. It doesn't affect much.
5. NO