Raise the flag (4)

I believe the answer is:

jack

I believe this is a double definition.

'raise' is the first definition.
(jacking is a kind of raising)

'the flag' is the second definition.
(jack is a kind of flag)

(Other definitions for jack that I've seen before include "Raise" , "Knave; raising device" , "Playing card; sailor" , "Name for sailor" , "Target ball in bowls" .)

I've seen this clue in The Times.

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