Several Stackexchange meta sites are reporting that there will be an optional event where one could earn "hats" for your gravatar (profile icon) to wear.
See these questions for details:
https://softwareengineering.meta.stackexchange.com/questions/5240/do-we-want-hats
https://workplace.meta.stackexchange.com/questions/525/do-we-want-hats
https://academia.meta.stackexchange.com/questions/287/winter-bash-holiday-hats
Should we participate in this fun event?