India, April 26 -- The power of the gesture is extraordinary. Well-used, it can be the fastest way to communicate an idea or emotion. Misused, it can be the quickest shortcut to cross-purposes, misunderstanding and hostility.

As a motorist in the UK, for instance, hold two fingers up in a V, palm facing outward, as you give another motorist right of way, and they will smile broadly, happy to have encountered a polite and peace-loving person. Hold up the same two fingers but with the palm facing inward, and it becomes a gesture of contempt or defiance. The inward-facing palm is taken so seriously, it has sparked incidents of road rage in England.

In France, meanwhile, press the thumb against the fingertips in an upturned hand and it indi...