Almost everyone knows about using signature lines for SEO and backlinking.
However, you can use forum signatures as a form of advertising to attract real visitors to your site.
Even if you are just using your signature line as a form of advertising (such as where people see your link and click on it), it's still important that the forum be similar in niche to your site, otherwise click through may be low.
So for instance, if your site is about sports cars and you post a backlink in a cooking/recipes forum, you're not likely to get many click throughs as the people on that forum are looking for info on cooking.
Please share any other techniques you have for using forums for advertising (not just SEO/backlinking).