Doodles
Doodles what are they?

Doodles are the fun, surprising, and sometimes spontaneous changes that are made to the Google logo to celebrate holidays, anniversaries, and the lives of famous artists, pioneers, and scientists.

In 1998, before the company was even incorporated, the concept of the doodle was born when Google founders Larry and Sergey played with the corporate logo to indicate their attendance at the Burning Man festival in the Nevada desert.
Some are even playable Apps.

Want to see some then http://www.google.com/doodles/finder/2013/All%20doodles