Google likes jokes, but it has confined most of the Android gags to one specific place. When you open the secret version logo, you can long press to see what Google has cooked up for an Easter egg. In KitKat it was an interactive mosaic of platform logos, in Lollipop it was a Flappy Bird clone, and in the M preview it's a shrug emoticon.

To see the shrug for yourself, you have to go into About Phone (or tablet) and tap a few times on the Android version line, which just says M right now. The materialized M logo that pops up can be long-pressed to activate the Easter egg. You get ¯\_(ツ)_/¯ in a toast notification. That's it. Might as well have been a trollface, Google.

The Easter egg often tells you something about the name of a platform, so obviously the preview secret isn't final. The L preview last year had the web driver torso animation as the Easter egg.