Yahoo is pulling out its biggest gun in the showdown with Carl Icahn: the Yahoo homepage itself. Right now on Yahoo.com, the single most-visited page on the Web (with 304 million unique visitors worldwide in May, according to comScore), there is a big purple button the third box down aimed squarely at Yahoo shareholders. The button takes people to this page where Yahoo outlines its argument against investor Carl Icahn, who wants to replace Yahoo’s board, fire Jerry Yang, and then restart negotiations with Microsoft (an effort that is not going so well).

Yahoo is in a battle for its life, and it is using the reach of its homepage as a weapon in its proxy battle against Icahn. It is trying to persuade every single Yahoo shareholder to vote against Icahn’s proposal to replace Yahoo’s board. Yahoo is going straight for Icahn, attacking his credibility as an investor. At the top of the “proxy facts” page that the button takes you to there is the following quote:

“It’s hard to understand these technology companies.”* – Carl Icahn

Then Yahoo reproduces one of the slides that it filed with the SEC at the end of June, which shows Icahn’s dismal track record recently as an investor (which is an easy trick in this market):

All Yahoo has to do to defeat Icahn is convince a majority of voting shareholders that he is wrong and not qualified to control the fate of the company via his hand-picked board. Taking the battle to the homepage shows how close it may turn out to be. Every single vote counts, and Yahoo is not shy about using its Web real estate to put up a sign arguing its case. It doesn’t say much for the editorial independence/neutrality of the homepage, but when you are fighting for your life those sorts of considerations are thrown out the window.

Update: Yahoo has already convinced one of its biggest shareholders, Legg Mason’s Bill Miller, who just announced that he will vote his 4.4 percent stake in Yahoo to support Yang and the current board. If Yahoo’s biggest shareholder, Gordon Crawford, does the same. It’s game over for Icahn.