Well, since ear plugs like that go back to ancient Indo-Europeans... we can talk about it here!
Yes, the design is usually a round disc with a groove in it. I would imagine steel plugs to be a bit heavy.
I'd say that plain carbon in constant contact with skin is not a good idea, which is why I lined my carbon damascus rings with Sterling or gold. About 25% of my customers had tarnishing on the rings which in a couple cases, also tarnished the neighboring fingers. I wasn't able to figure out whether it was environmental, biological or what, but I do suspect it had something to do with changing alloy contents, as the rings didn't do it at all when I started making them four or five years ago.
In any case I use all stainless damascus now.