Does it count for nothing in the Secret Service? (6)

I believe the answer is:

cipher

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

'nothing in the secret service?' is the definition.
'cipher' can be an answer for 'nothing' (synonyms). I'm unsure of the 'in the secret service?' bit.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for cipher that I've seen before include "Key to a code" , "Code - 0" , "Symbol representing nought, thing of no importance" , "Nonentity" , "nobody" .)

I've seen this clue in The Irish News.

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