Currently, there is no tag for "secp256k1".
Given how important Bitcoin has become, it might be time to have such a tag.
Doing so would make it easier for users to find and answer secp256k1-related questions.
No, we should not introduce a secp256k1 tag. Just a single curve specification is too specific to merit a tag of its own. Instead we could introduce a koblitz tag, as the curve is associated with a Koblitz curve.