It depends if the contents of your site, are solutions to problems that the users have, because, if it offers solutions, it can generate traffic, but, maybe not much as you would like to. Choose where to use your site link. But it's more usefull if you are looking for information, that you provide in your website.
This is really a good question. I have accounts in almost 10 popular forums and i post about 5 posts to each of them every day. In my experience, the forum signature bring few traffic to my site, usually less than 10 in a day.
Forum signature are helpful to get traffic to your site especially if you able to find relevant for your niche. Since i am enjoying different conversations in the forum, i consider it as a guide since i learned new things to other forum porters and it is a way of discovering new post and new knowledge topics.
i do completely agree with this as if you posting your comments on fashion and you are providing a link of web development then though you have a nice post yet people will have less tendency to click to it and follow your link. So try to post on a niche topics if you are expecting visitors from forums.