The ability to track tag badges is a new "privilege" bestowed upon Trusted Users (20K reputation here on math.SE). See the following Meta.SE question:
Essentially, once you have no more privileges to track, you can track tag badges in that now useless spot. (I imagine that something similar happens on meta: there are no meta-specific privileges to earn — beyond the ability to participate on meta, which is still a main-privilege — so they display tag-badge progress there.)
The "poor person's" method of tracking tag-badge progress is to go to the tags tab in your user "activity" profile.
If you hover over the number to the left of the tag-name, a tooltip pops up telling you the number and cumulative score of all non-CW answers you have posted in that tag. (Additional information may also appear.) We then have to remember the criteria for tag-badges, as listed in the Badges page from the Help Center:
- Bronze. You must have a total score of 100 in at least 20 non-CW answers to achieve this badge.
- Silver. You must have a total score of 400 in at least 80 non-CW answers to achieve this badge.
- Gold. You must have a total score of 1000 in at least 200 non-CW answers to achieve this badge.
No fancy bars, but it does the trick.
(Boy am I tantalisingly close to that bronze axiom-of-choice badge!)