tell me if this situation would give me a good link and help my page rank: Lets say i join a forum and make one post with my signature having a link to my blog. If i were to click my blog link, would that count as a link from that site and would that help my pagerank. Obviously this would not help much with traffic but would it give me a good link and help my pagerank?
Forum sig links help a bit... but you might / probably will piss off the admins/owners if you do not stick around a while before adding your link etc and so on. Find a forum that you are interested in, post a little...then do your thing. There was a thread here about good guidelines on this recently.
once single backlinks from forum will neither give you traffic or help you in PR. it may or may not give you a backlinks depending on whether the individual post where your commented with your signature gets indexed or not and whether googlebot follows your link form that page. you clicking on the blog link would not make any difference.
if your question is will it be beneficial and good for your site. the answer is YES. it will do good in your site. Signatures on forum threads do help drive traffic to your site. IMO try enagaging to a high conversation site and put an eye catching signature anchored to your site. one post i see is his signature is "LeBron james heading to Chicago? That sux!".. this is just an example, i suggest you think outside the box.