TURNS OUT THIS ALREADY EXISTS. NEVERMIND
So we have all sorts of tags representing all sorts of topics. Naturally some people are more skilled/knowlegable in terms of some tags than others. Wouldn't it be nice to be able to say "Look, [potential employer/peer/anyone worth impressing], StackOverflow says I'm pretty good with [insert tag name here] specifically, and this is why ..."
A badge for earning a total x reputation for questions and answers to do with a single tag. This badge can be earned once per tag or group of tag synonyms. Maybe have it that there are bronze, silver and gold badges available for each tag. So someone could earn a bronze badge for Python, then a silver, then a gold when they have proven their awesomeness.
A badge for getting x answers accepted for questions with specific tags. This badge can be earned once per tag or group of tag synonyms. Again there could be three badge levels with this. Bronze for just a few accepted answers, and gold for 'this person might as well have invented [insert tag name here]'
A badge for earning x reputation just from answers (accepted or otherwise) to do with a specific tag etc etc...
I know tagging is often not an exact science. And people can edit tags on other people's questions which could leave this open to abuse. I still think it would be a pretty cool feature.
The fact that these badges could well be useful in showing a person's skill level in specific areas could have real-world implications (like employment stuff). This creates a bit more incentive for people to provide higher quality and more numerous answers in the fields they consider themselves expert in.
What do you think?