That is the standard JIC wiring diagram symbology for selector switches. JIC standards have gone by the wayside I guess.Really poor way of doing it. Should be labeled "3SS A, B, C with a note that says it's shown in the open position. If that's really what they are trying to say.
What do the three arrows mean??
I have most often seen it as a series of "x" and "o", with "x" for closed an "o" for open. Next to a contact of a 3 position selector switch contact that is closed with the selector in the left position, it would be "xoo" and next to the a contact that is closed in the right position it would be "oox". I have never seen what is shown in this drawing.