One of the goals with the (non-)architecture of umbracoStats where to make it possible to do "tracking-mashups" in terms of making umbracoStats do things that wasn't originally the purpose.
Yesterday I discovered one way of doing that, by "hacking" (in the positive meaning) the newsletter for tracking links in my outlook signature :-)
So here's an easy 3 step guide for doing that!
1. Create a page on your website where umbracoStats is installed.

Name it something like "E-mail signature tracking" or whatever make sense for you. Remember to create it in a part of your website that aren't displayed or hide it in the navigation.
Hover over the new document in the tree part of umbraco, and look in the footer; this will display "javascript:openContent(xxxx)". Now the xxxx number is the id of your new place and we'll need this for the next step:
Step 2: Add tracking to the signature link

Edit your e-mail signature and add this to the link: "umbNl=xxxx" where xxxx is the id of the page in step 1 (you can often have separate link and linktext, so the confusing tracking code aren't displayed as a part of the visible link).
Step 3: Start tracking :-)
That's it. The moment people start clicking the link it will be visible in umbracoStats and you can monitor if the signature-link has any effect:

(as you can see I haven't sent enough e-mails the past 24 hours :-))
A step further: Not only for e-mail signatures
This technique is not limited to e-mail signatures, but can be used in many other places. Happy stat'ing