The signalman's girl (4)

I believe the answer is:

alma

I'm a little stuck... Click here to teach me more about this clue!

'girl' is the definition.
(girl's name)

'the signalman's' is the wordplay.
'ALMA' is hidden within the letters.
But, I'm unsure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for alma that I've seen before include "dancing girl" , "One's university" , "Woman" , "Loving girl" , "Battle of the -- was in the Crimean War" .)

I've seen this clue in the Evening Standard.

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