Just a couple of dots for future reference

From Deadly Illusions: The KGB Orlov Dossier Reveals Stalin's Master Spy by John Costello and Oleg Tsarev,

The practical tricks of the trade including how to throw off police surveillance by making convuluted journeys-- switching public transport between buses and taxis was a favoured method. When it came to passing documents to contacts, libraries and the dark interiors of cinemas were favoured.. According to Orlov, the OGPU in the 1920s and 1930s favored particularly the use of the surgeries of 'trusted dentists and physicians', which were the preferred sites for really important meetings.