If your website is made in flash, or have components that do not play well on mobile devices, Google will leave clear.
What you see on above picture is an example of what displays Google search engine when returning a website that uses Flash, a text alert that the contents are not visible from mobile, an alert appears on the pages that appear white or do not show much of its contents, when they are not compatible with these devices.
Importantly, this ad will not appear when a website does not have a specific mobile version, only show when the content of the page does not appear, not when it appears with little or no letter suitable for small screens.
I commented on the blog google webmaster while recall a couple of resources recently announced:
– Web Fundamentals : A good place to share best practices in the development of modern web pages.
– Web Starter Kit : A framework to help develop websites using resources compatible with any mobile device.