• by Laurie Sullivan , Staff Writer @lauriesullivan, June 25, 2013

Letters have been sent by the Federal Trade Commission to more than 20 search engine companies making clear that they must distinguish paid from unpaid listings. The update to the 2002 published guidance urges companies to make a strong distinction for all forms of advertising, including product listing ads and search in Facebook or other social sites.

The FTC in particular calls out "general-purpose" search engines AOL, Ask.com, Bing, Blekko, DuckDuckGo, Google, and Yahoo, as well as 17 of the most heavily trafficked search engines that specialize in shopping, travel, and local business, and that display advertisements to consumers.

U.S. advertisers will spend nearly $19.5 billion on paid search this year -- up 12.4% compared with last year, according to eMarketer. Google garnered $12.79 billion in net U.S. search ad revenue last year, or 73.8% of the total market. The research firm estimates that Yahoo will generate $1.27 billion this year in net U.S. search ad revenue, or 6.5% of the U.S. total, compared with Microsoft at 4.6% -- up from 3.8% in 2012.

Clarity remains the No. 1 priority. The updated guidance requests an increase in visual cues like color, shading, labels or other indications that distinguish the advertisements from organic listings. The FTC points to Search Ad Awareness research from SEOBook that highlights the confusion when using different colors, positions and more.

Those visual cues must appear on the Web as well as on the mobile devices the ads render. The FTC believes Web pages should use "different luminosities" for mobile devices compared with desktop computers.

As search evolves, one of the more interesting requirements points to the disclosure of voice ads. "... if a voice interface is used to deliver search results, a search engine should make an audio disclosure that is of an adequate volume and cadence for ordinary listeners to hear and comprehend it."