Just to elaborate and clarify, there are a few different types of pizzicato:
- There is the standard "pizz." which is done with the flesh of the finger on the bowing hand;
- A pizz with fingernail, which gives a more crisp attack;
- A "Bartok" or "snap" pizz where the performer pulls the string away from the fingerboard and releases to produce a harsh snapping sound;
- A left hand pizz which performers may do while performing simple or thoughtfully written passages;
- There is also strumming, which is notated with "pizz", an arrow to show direction, and usually an indication of "quasi chitara".
I thought it important to mention these things because the OP included the word "fingernail" in their question, and that is a specific type of sound that is not the standard pizzicato (in that it would need indication.)