There is one thing you should keep in mind never use same anchor text on too many forums, like if you have used the anchor text in 200 forums then change it for other forums because it might look like auto postings or submissions. Forums signatures are good for traffic as well; if you have something useful in your anchor text people will visit your website. Forums signatures are counted as only 1 backlink, if you have made 500 posts in forum and you are a regular member, it does not mean you have 500 back links only 1 link will be counted as back link. Usually forums are good for traffic rather than backlinks, there is also one more thing only do follow forums will give you benefit of back link. If you have joined no follow forums then there is no value of signatures other than traffic you get from your signatures.