A visual indicator assembly displays the state of an isolated stem control valve contained in a housing of an air tank. The visual indicator assembly comprises a rotatable handle member adapted for operative connection to the isolated stem control valve contained in the housing of the air tank. The rotatable handle member opens and closes the control valve without axial movement of the rotatable handle member. An “OFF” indicator is visible with the control valve in a closed condition, and an “ON” indicator is non-visible with the control valve in a closed condition. The “ON” indicator is movable to become visible and obscure the “OFF” indicator upon rotation of the handle member to adjust the control valve to an open condition.