They are considered to be devalued and not have a large impact on organic search results. However, they do still have "some" value and should be used in a supplemental link building program. If the forum your signature is on is relevant to your website they will also help drive traffic to your website. I don't recommend putting links in a signature that have no relevant content to the forum itself.
premierwebstrategies is correct. Links in forum signatures carry VERY LITTLE weight for SEO purposes. However, they can carry some weight for generating traffic. If you particpate on online forums related to your niche, you should see some descent FREE traffic coming in from those forums signatures.
I am measuring forum links as quality backlinks. I think, if you are in a relevant forum, relevant to your business, finally you are going to get results. To start with, forum links are LINKS And they are increasing PageRank.
The value of forum links in seo is too because this genrate a alot of traffic in your site you recived a backlinks in diffrent forums.
Backlink is backlink, basically the different is on the quality of the site, not the type of the site
It is good for gaining initial rankings for new websites. It is like getting a shot in the arm. Other than that links from signatures tend to be buried easily with more new posts being posted.
It is one most important technique in SEO, it will help you in gaining traffic as well help in gaining good PR very quickly.
Thanks for the replies everyone, I have a list of forums where signatures are DoFollow, but before I spend a lot of time on them I want to make sure its going to be worthwhile.
It's less of forum vs blog and more of forum quality vs blog quality. If a forum has some PR and you create a profile it might rub off to your profile and at least get you something. If you are talking strictly in threads links then they are considered backlinks but besides diversifying your backlink makeup are of little worth.