<p>For the logo, another option would be to show a scatter plot with a best-fit line through it, possibly using a non-linear relationship (like loess) as <a href="http://learnr.files.wordpress.com/2009/08/chapter05-05_09_r.png" rel="nofollow noreferrer">in this example</a>.</p>

<p><img src="https://i.stack.imgur.com/kwna5.png" alt="alt text"></p>

<p>This has nothing to do with cross-validation, but it would certainly communicate the purpose of the site.  I prefer <a href="https://stats.meta.stackexchange.com/questions/269/what-should-our-logo-and-site-design-look-like/458#458">the other option above</a>, because beyond everything else it will be clearer.  </p>
