Fù zhǐ 复指 (trad: 複指) “Repeated Finger”
A class of techniques where the same string is struck twice in quick succession. Either the same finger or two different fingers can be used. The symbol is a combination of the individual techniques stacked on top of each other.
The following list is offered by Ferguson and personal experience:
Thumb, closing then opening.
Middle finger, closing then opening.
Thumb then index, both closing.
Index then thumb, both closing.
Thumb closing, index opening
Index then thumb, both opening. Ferguson calls this Gǔn zhǐ 滚指, “Rolling Fingers”
Middle then index, both closing
Index then Middle, both closing
Middle then index, both opening.
Index then Middle, booth opening.