Is Marissa Mayer about to go to war with Google in search? These screenshots suggest yes

We have some fascinating screenshots of what looks like a new user interface for Yahoo's mobile search engine.

They make you wonder: Is Yahoo CEO Marissa Mayer is about to push Yahoo back into a search war with Google?

In 2009, Yahoo signed a deal to outsource its search business to Microsoft. Ever since the alliance was implemented in 2010, all Yahoo search pages said they were "Powered by Bing." That included mobile search results pages, even though mobile search was not technically included in the Microsoft-Yahoo alliance.

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Here's what a typical Yahoo mobile search results page looks like. Note the "Powered by Bing" branding on the bottom right:

Yahoo Search

This is what the new, still-being-tested Yahoo search screenshots looked like. Note that "Powered by Bing" is not on any of the screens.

Yahoo

It's hard to pin down what, if anything, it means that Yahoo's test search results pages don't have Bing branding on them.

On the one hand…

• A search industry source told us the actual results on the test search results pages appear to be the same results that a Bing-powered Yahoo mobile search would surface.
• Even though Yahoo's mobile search engine currently uses Bing, the Microsoft-Yahoo search deal never included mobile search. Yahoo could stop using Bing on mobile search and continue its desktop deal with Microsoft.

On the other…

• A couple weeks ago, a person who claims to have been working in Yahoo's search division until recently told us that, under Mayer, Yahoo built its own mobile search engine. This source that Yahoo was testing it with 15% of its mobile users. We've been unable to corroborate all of those details, but - thanks to instructions from that source - we were able to able to load the new version of Yahoo's mobile search engine.
• Yahoo's search results pages included Bing branding until now. Why would that branding suddenly go away?

Perhaps the Bing branding is going away because Marissa Mayer wants to make Yahoo a player in search again.

Few people remember it now, but for a time - around 2005 and 2006 - Yahoo was a serious competitor to Google in search. But Google was better at yielding revenue from its search ads, and it used the extra cash to pay for search distribution across many portals. Soon, Google had an effective monopoly.

In 2009, Yahoo threw in the towel and outsourced its search business to Microsoft Bing in a 10 year deal.

The deal quickly proved to be a disappointment. Yahoo's search share eroded, and Microsoft's only seemed to grow as much as Yahoo's shrank.

When Yahoo hired Mayer in 2012, many assumed that the former Google executive would get Yahoo back into the search business as soon as she could.

More recently, there have been whispers that, halfway through through the deal's 10-year term, Yahoo and Microsoft are back at the negotiating table. Supposedly, Mayer is pushing hard to find a way to end the alliance.

Finally, there has been a lot of analyst speculation that Mayer is planning to out-bid Google for the right to be the default search engine in the Safari browser on iPhones and iPads.

Despite all that speculation, however, we still cannot go so far as to say these screenshots prove that Yahoo is going to break up with Microsoft and launch its own search engine.

Through a spokesperson, Microsoft declined to comment on this story.

Briefed on the details of this post, a Yahoo spokesperson says, "Search is an important part of Yahoo's business and we're always experimenting and looking to improve the experience for our users. We have nothing to announce at this time."