Within intelligence communities, spycraft refers to the techniques used by spies to gather intelligence and remain undercover. The need to manipulate, discover, and remain secret has spawned the time-tested techniques used by spies everywhere.
I used these methods throughout the Dark Talents trilogy, set in England in 1936. Here are some examples culled from Kim Tavistock scenes in Book two, Serpent in the Heather.

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SIGN OF LIFE. To confirm with handlers or HQ (the “office” in British intelligence service parlance) that one is on duty and pursuing the mission.
In a wool skirt and sweater set Kim made her way down to the castle parlor, where she put in her call to Knightsbridge and Nash Photo Finishing. Someone from the Office answered appropriately and said her photo prints would be ready on Wednesday. Her sign-of-life call complete, she turned to find Powell had entered the drawing room.
THE COVER PERSONA. Obviously, spies wish to remain undetected as such. To that end, they adopt ostensible business and deflecting personal attributes.
“Tread carefully with this Coslett woman, Kim. We’re only allowed a limited operation. You must deploy your witless- American mode to perfection.”
She snapped a look at him. “I didn’t know I had one.”
“What? Oh, yes, quite a good one. Charging around all innocent and eager. Top-notch.”