This question already has an answer here:
I noticed that there's a small black line through the bronze badge display on my Meta.SE profile, as shown here:
I've also seen it on Shog9's profile. It's on some, but not others.
On another profile, the line shows up under the silver badges:
This showed up on another user's profile, too.
I have yet to see it on the gold badges, but I haven't searched that many profiles.
My browser is Internet Explorer, so I don't know if it shows up on other browsers.