I do not think you can create animated signature but you can create animated avatar. Animated avatars are annoying and the more you see more people using it the more annoying the avatars become. Animated signature will be worst.
At one time animated avatars supported forum accounts. And those who put up animated avatars back then still have them on their profiles. And it supports. But the new animated avatar can no longer be added to the profile. Because now it is closed so no user can use animated signature or avatar in his profile even if he tries hard. they are not yet possible it now