Dio's two-finger gesture - what does it mean?

It's a gesture commonly seen at rock concerts. The index finger and the little finger are upright and the thumb is clasped against the two middle fingers. Ronnie James Dio, who sang with Black Sabbath and Rainbow before forming his own band, was partly responsible for it becoming a common symbol among metal fans. But it has other uses too, depending on the position of the thumb, and the context. Here is a round-up of some of the common meanings.