You were letting the other members of the site you are working with,
and not only that everytime you post an interesting and helpful posts
there is a possibility that you might get their attention to see your sig.
For me forum sigs serve as one way of advertising your site. Or share some useful notes or quotes that might help other people. Or simply a place of expressing yourself That's what forum sigs for me
__________________ It only takes one Google search
Forum sigs are just one part of any seo plan - they are not very important but they might make a difference and when you are in a competitive niche surely any edge you can get is worthwhile.
Forum signatures does not only bring in direct targeted traffic overtime, they also help in SEO. The way you participate in those forums would have a final say on how it would affect your sites IMO.
I was able to make our directory rank for relevant keywords solely through forum sigs. This was a bit of an experiment I did before.
If anyone is newly acquainted to forums then one must know that Forum Posting is one of the best ways to get site noticed. In this process, what we have to do basically is just give the link of your website as a signature. It is also to be noted that one has to look where there are more number of participants in the site.