Old world hand gesture (a clenched fist with the index and pinkie fingers extended) used to protect onself from the "evil eye" or to project the "evil eye" onto someone else.
Popularized in the 1980's by Ronnie James Dio (Rainbow, Black Sabbath, Dio) while on tour with Black Sabbath in support of their Heaven and Hell album.
A hand gesture that is frequently misused when displayed at concerts that do not fit into the metal genre (or any of it's many sub-genres).
Throwing up the mano cornuto for Alexisonfire? Unexceptable.
Throwing up the mano cornuto for Nickelback? Unexceptable.
Throwing up the mano cornuto for Pantera? Mandatory.