[Newell Attack]

I know that it's helpful to truckers to have the vehicle they just passed flash his headlights to show that it's safe to pull back in to the right-hand lane, but here is my question: Is it correct to flash your headlights BEFORE the passing vehicle puts on his right turn signal to show his intention to pull back in, or IN RESPONSE TO his signal, as if to say, "OK c'mon back in"?

Jeff