Last modified: 2014-06-02 02:47:46 UTC
The community has voted to disable images in signatures on the site.
Same as bug 36371 and bug 36372, unless I'm mistaken, there is no way in MediaWiki to currently do this..
This currently has to be implemented and enforced as a local wiki policy. If a technical way is wanted to enforce that, a bug should be filed as an enhancement against MediaWiki to implement this functionality/restriction.