Green’s Dictionary of Slang

dipping duke n.

[dip v.2 (1) + duke n.3 (1)]

(UK Und.) the hand with which a pickpocket works.

[UK]Leaves from Diary of Celebrated Burglar 70/2: Iv uz keeps on at this gait there’l be nowt left for that ‘wire’ an’s mob way sprayned his ‘dipping duke’.