Under [Options|Music|Instrumentation] you can further specify how these characters should appear on paper in terms of color, size and font.
To prescribe 'plucking' with the fingers, a technique called pizzicato, notate pizz. or in full pizzicato above the part. To indicate that it is time use the bow again, write arco. Use directions 4 to add arco-like texts.
In sheet music for strings, legato is frequently used, essentially legato arcs that indicate which notes should be played one bow.