I see no concrete reason why there should be badges made for posting milestone or merits received.
There is enough motive to seek to gain merits, and I don't see why we should enocurage people to post to get badges

Reporter badges would be to encourage members to use the 'report' button and also to reward those who already use it

Reporter statistics are not public, unlike post count and merits which can be viewed in the profile and determines the members rank and ability to wear, avatars and signatures.