What influence does a signature link from the UKBF's site have on my site?
The first page of this thread has about 170 links on it, of which a single post's signature link might be one of those links. The prominence of this thread is also short lived, it is a few clicks away from the home page now, but in a week, a month or a year's time it will be less prominent, many clicks away from the home page - today's newspaper tomorrows chip paper.
So on the grand scale of things, forum signature links do not have much SEO value. If they are on pages which are not relevant to your website's targeted terms then they offer even less value. If you've posted thousands of posts, then thousands of the same signature link from the same website are not going to provide much SEO value either.
But sometimes they can provide a little value, and they can still drive traffic to your site from real website visitors. If you are on a relevant forum regularly talking about relevant things, relevant as in relevant to your website and services, then signature links should help both in an SEO sense (a little) and in a driving relevant traffic (a lot).
Advice you give on a forum is not only picked by the people (members and lurkers) reading the forum at the time the advice is given, but it may be picked up by people googling for such advice in the future too, they find the forum, your posts, and if they like what they read, they might want to contact you or visit your website.
One other thing to mention, is the link in the popup menu when you click on the member name link top left of the post, the "visit member's homepage" link, which is also a link which google might pick up (even for free members and spammers, Sift take note!), and also useful for real visitors.
