Discussion boards are great place to tap into your target audience. They are where people hang out. Approaching such a forum strategically, you can drive traffic back to your website quite easily. Many people blatantly promote their site and this is exactly the opposite way to do it. You want to contribute and build your name first. After you establish your expert status there, whatever you put in the signature in the forum, people will visit because they know you provide solid advices and content related to the topic of the forum.