1. The French title of HCB's most famous book is Images a la sauvette, literally pictures on the fly or on the run.
2. For the book Magnum Streetwise, about street photography as practiced by Magnum photographers "...To be able to approach such a scene, unobtrusively get within camera range and take one or two frames, and then depart leaving the subjects untroubled and the location untouched is akin to being a cat burglar."
3. I don't have the direct quote, but in the film Don't Blink, Robert Frank talks about having to hide his camera when he went into some of the bars to take photos, that the crowd was rough.