Mark is badly shamed (2,4)

I believe the answer is:

em dash

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'mark' is the definition.
Both the definition and answer are singular nouns.
Perhaps they are linked in a way I don't understand?

'badly shamed' is the wordplay.
'badly' indicates an anagram (letters in the wrong order).
'shamed' anagrammed gives 'EM DASH'.

'is' acts as a link.

Can you help me to learn more?

I've seen this clue in The Independent.

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