From
https://www.google.com/adsense/policies....
Ad Placement
* Up to three ad units may be displayed on each Web site page.
* A maximum of two Google AdSense for search boxes may be placed on a page.
* A single link unit may be placed on each Web site page, in addition to the ad units and search boxes specified above. Link units are considered to be 'Google ads' for purposes of these program policies.
* No Google ad may be placed on any non-content-based pages.
* No Google ad or Google search box may be displayed on any domain parking websites, pop-ups, pop-unders, or in any email.
* No Google ad may be placed on pages published specifically for the purpose of showing ads, whether or not the page content is relevant.
* Elements on a page must not obscure any portion of the ads, and the ad colors must be such that any ad elements, including text and URL, are visible.
* Clicks on Google ads must not result in a new browser window being launched.