All you do is add ?trackingcode after any URL.

For example, if I wanted to track which forum sends my traffic, I may add URLs like these to my sigs:

http://www.tuelz.com/bigpage.html?dombom
http://www.tuelz.com/bigpage.html?warrior

Just add each to your sig for the appropriate forum, then check your stats for each "page", as servers will "account" for these as two seperate URLs.

There is one drawback - The engines may well see these URLs as "dupes", so keep this in mind.

This also works for email subject lines embedded in links:

me@mydomain.com?subject=DomBom

If you create an email link like this, "DomBom" will be automatically inserted into the subject line of your email...A great way to track where you're email address was found.