On certain occasions, the logo on Google's webpage will change to a special version, known as a "Google Doodle". Clicking on the Doodle links to a string of Google search results about the topic. The first was a reference to the Burning Man Festival in 1998, and others have been produced for the birthdays of notable people like Albert Einstein, historical events like the interlocking Lego block's 50th anniversary and holidays like Valentine's Day.