As Google said, blog comment links are almost worthless, you need many hundreds to have any effect.

Now, how about forum links in your signature?

I don't think they are worthless but their overall affect on your search rankings will be small. If you participate in forums and leave relevant comments then people will eventually want to link to you or visit your site. I think the same approach can be taken to blog comments.

I should imagine forum sig links are even more worthless than links from blog commenting, at least with blog commenting someone has actually put some effort into creating a supposedly interesting article, most threads on forums start with a 2 or 3 sentence post, thats hardly going to inspire the bots is it.

If you're going to participate in a forum, I don't see any harm in having signature links. You might as well. However, if you're looking to boost your site in the search engines or trying to generate a lot of traffic, you're wasting your time.

imo,it useful for promotion our site,do follow blog comments could get us backlinks,post comments on relate blog also could get us traffics.

Sig links in Forums rarely worked for me - and if they did, I was doing other things like on-page optimization. Sig links in forums (especially niche forums) are great for advertisements, but not for SERP climbing.

http://www.webmaster-talk.com/seo-ta...-no-value.html