The idea hit me today when considering moderating a chat for inappropriate behavior: Have role-specific emojis which are identified by a colored border (which would correspond with that assigned role) and is additionally only usable by that specific role.
I.E.: The moderators in a server I participate in are given blue names. Accordingly, the role-specific emojis would—aside from being unique compared to the server's "public" emojis—be readily identifiable if applied to someone's message. Others could vote it up, but they wouldn't be able to use it themselves.
In practice, what could this be used for? In my specific example, if someone is pushing the rules but not quite breaking them, it would be both an easy and funny to "mark" someone's offending message with such an emoji; it would be a quick, easy way of letting them and those around them know that they're not as under the radar as they think, without needing to take time to just drop in a message to warn them unless they're really going over the line.
Beyond such a use as that? I honestly have no idea, but I'm sure others could think of additional applications of such a feature.