Found in the Haining collection - this article from 1936 on pickpockets. The author Louis Mansfield has much advice,most still relevant. The bit about a 'dip's' long, tapering fingers may be fanciful but certainly it is not a profession for one with fat fingers...
PEARSON'S WEEKLY, May 30, 1936
THIS IS DERBY WEEK, SO–WATCH YOUR POCKETS!
Pickpockets will be busy among the crowds. It is their best time of the year. Louis C. S. Mansfield, detective and crime investigator, lets you into secrets of the "dip's" profession – and they have some good ones. You have been warned!