That's actually an ad, but not one that we're running.
Please note that it's possible for ads to appear in your browser that were not placed there by WordPress.com. These ads are sometimes caused by malware or a virus, but more often it is due to a browser extension or toolbar that you may have installed in your browser.
These sites have further explanation and suggestions for eliminating the ads:
http://onecoolsitebloggingtips.com/2012/09/14/bloggers-beware-of-adware/
http://www.littletechiethings.com/2012/06/how-to-remove-ads-not-by-this-site.html
http://blog.wikimedia.org/2012/05/14/ads-on-wikipedia-your-computer-infected-malware/
I hope this helps! Please let me know if you have any further questions.