Signature links are appearing for each and every post. But my doubt is "Whether google consider signature link as backlink to the site" Is there any PR improvement with Sig. link?
Every link that doesn't have the "NoFollow" tag is considered by Google. Some links have greater value obviously (those from old established & authority sites).
Sig links are "do-follow", but almost all forum threads here are PR0 or unranked, so you won't really gain much from them other than fast indexing and good traffic
i would be interested to look at a site that solely had tons of forum links and see how it was doing. I've considered doing an expirment like this, but never got around to it.
Sig links are considered as back links.They are only help to get more traffic will not help to improve ranking.