Currency unit in Costa Rica is the mark (5)

I believe the answer is:

colon

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'currency' is the definition.
(I have seen 'Foreign currency' mean 'colon' so perhaps 'currency' could also mean 'colon')

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for colon that I've seen before include "Part of body; some punctuation" , "cash" , "cut short dependency?" , "Stop - part of intestine" , ": - bit of the gut" .)

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

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