Is I have 1500 post on a forum and if I enable signature with my link in it then I will get 1500 backlinks from that site will that improve SEO or will hurt it. Signature backlinks are dofollow!!!!!
I would say they're worth it, especially on high PR forums. Dropping a link in your signature and posting useful posts is sure effective. The forum doesn't need to be related to your keyword, just post on forums you have interest in, you'll kill two birds with one stone. However, if you find a related forum which you have no interest in, you can always make one useful post and let it be.
You will be fine. Other good strategy is to rent other people's forum signatures then diversify the anchor text.
In general it should be good for SEO as long as all of your backlinks are not from forums. One thing that should be mentioned is that in many forums renting your signature is against rules. Make sure that you don't get banned for it.
I have a few good dofollow relative backlinks from that site/forum so I probably not going to risk it I have just recovered from one update so can't imagine getting penalized again. Thank yo very much for your support. The forum is more or less relative to my forum.