You might notice a slight change in Twitter today: Sponsored text ads now appear underneath the “trends” column on the Twitter home page. The format includes a URL linking to the sponsor’s site and a related Twitter hashtag to “follow the conversation.” That spot had previously been used to promote Twitter-related services or apps, but now links to third parties like the NFL.
Labnol, which reported on the appearance of the ads, was surprised that Twitter doesn't specify on the page that these are sponsored links or ads, or use a “nofollow” tag. The only mention that there are actually advertisements is within the HTML source of the site.