Hackney's hackneyed according to quotation spotted on mug (5)

I believe the answer is:

acned

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'spotted on mug' is the definition.
'acned' can be an answer for 'spotted' (I've seen this before). I'm not sure about the 'on mug' bit.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Another definition for acned that I've seen is " Spotted".)

I've seen this clue in The Independent.

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