Snap pizzicato (“Bartok” pizzicato)
A snap pizzicato (also known as “Bartok pizzicato”) is a “strong pizzicato where the string is plucked vertically by snapping and rebounds off the fingerboard of the instrument” (Wikipedia). It is denoted by a circle with a vertical line going from the center upwards outside the circle.
\relative c' { c4\snappizzicato <c' e g>4\snappizzicato <c' e g>4^\snappizzicato <c, e g>4_\snappizzicato }