On violin and viola we only use four fingers to play (index finger is numbered first finger, pinky is the fourth finger) so there's no "fifth finger". I'm sure whoever penciled that in was a pianist -- their pinky is the fifth finger.
In any case, I love Mahler 1. The third movement, the funeral march, is just out of this world... I want this to be played at my funeral! When I played it with Waterbury Symphony about a year ago, tears came to my eyes because of the beauty and sadness of this movement. That doesn't happen very often (or almost never), I think the experience with WSO was almost a once-in-life-time event.