Yesterday, I find commenting on releveant forums with a link of my blog in signature is regarded as one of the best SEO technique. But unfortunately Iwhen I Tried few yetserday, i found that all of them after posting goes to a page where no page rank is there. In such cases can I expect backlink from them when google will find them?
Google will index the page, but as you mentioned, the PR will probably be ridiculously low. It makes no sense to have to work so hard everyday for your SEO plan.
Dont worry so much about PR. Think about traffic. If you make informative posts and include your links in the sig (or body) you will be likely to get traffic from it. Remember that your posts are permanent and forum posts often show up in search results.
Agreed with kentucky - the value in signature linking is not in Page Rank (usually) but rather in building a body of potential avenues to your site(s). Traffic will come if you continue to post in busy forums with relevant information.
Yes, its possible for your site to have backlinks specially if that forums is updated often with lots of threads.