I posted fairly often on certain boards and as for sigs, I've never sold mine, but I do tend to promote stuff that I use or my clients. I've noticed that it helps a bit in search engines because it offers many links to the site, and if there are keywords that relate on the page, then it's all better.

But I don't think you'll actually have any action from people clicking your link unless you are able to show that you DO know your stuff and not just someone with 500 "own3d" pics or something.