They review problem with motorway sign (9)

I believe the answer is:

summaries

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'they review' is the definition.
Although both the answer and 'review' are nouns, they are not in the same form of the noun.

'problem with motorway sign' is the wordplay.
'problem' becomes 'sum' (arithmetic problem).
'with' is a charade indicator (letters next to each other).
'motorway' becomes 'M' (as in motorway names - M1, M4 etc).
'sign' becomes 'Aries' (star sign).
'sum'+'m'+'aries'='SUMMARIES'

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I've seen this clue in The Guardian.

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