Gesture

[Glen]

Some friends from Mexico recently put a question to me that I had no answer for.
What is the significance in US culture of holding one's left index finger straight out and parallel to the ground - or pointed slightly downward - and rubbing across it with the straightened right index finger (as if peeling a carrot)?
The context they had for such a gesture was that it was done by some authority figure while pronouncing judgment on someone else.
Any ideas?