To ensure that, FIFA has been issuing DMCA complaints to Twitter about the offending avatars.
For the offending accounts, they’re profile image reverts to the Twitter egg until the user replaces it with something else.
In its guidelines for use of its official marks (PDF), FIFA states the following in regards to social networks:
FIFA’s official logos, symbols and other graphic trade marks may not be used on any social media platform. FIFA’s Protected Terms (e.g. the event titles) may not be used to create the impression that a page is officially related to the 2014 FIFA World Cup™.
If you’re thinking of using the FIFA logo, World Cup trophy, or that weird armadillo mascot as your avatar, don’t be surprised when it suddenly disappears.