Maybe someone knows... Why not prohibit the use of animated avatars if they are used for advertising purposes?
Only way to do that is to set the rule "no animated avatars in signature / bounty campaigns", or even for personal use if user is promoting something. But in such a way someone would have to control it, means more work for moderators.
The simplest way is to disable animated avatars for all users, which certainly is not a popular measure, but as it usually happens in today's world, the majority mostly pay for unreasonable actions of few people.
These animated .png avatars have certainly become more obvious over the past few days since the Stake.com bounty campaign started paying anyone for any old spam with no max post limit.