There seem to be a few badge oriented achievement modules in Drupal.
The more commercial one is based on http://www.badgeville.com/
The module is https://drupal.org/project/badgeville_gamification
Mozilla's OpenBadges is also interesting http://beta.openbadges.org/backpack/login
Also, there are comparisons & discussions about this.
There is also this User Badges module which can be assigned by role or by an adminstrator:
Would be useful to know who is implementing these and what the results have been from any of these approaches.
I think it could potentially be useful for drupal.org, but more interested in how they are working "in the wild" and what can be learned about using them.