A sign of free accommodation (4,2,3)

I believe the answer is:

room to let

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'a sign' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'of free accommodation' is the wordplay.
I cannot quite see how this works, but
'of' could be 'o' and 'o' is found within the answer.
'accommodation' could be 'let' (I've seen this in other clues) and 'let' is located in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Globe and Mail.

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