This is part of Hasse's "Mea Tormenta, Properate":
Figure 1. 3 staves of handwritten music. The top staff is in treble clef and the key of B flat. The second staff is also in treble clef and in the same key. It has no notes and just contains a caesura/simile like symbol (which looks like a pair of parallel diagonal lines) in the middle of the staff. The third staff is in alto clef in the same key. This staff contains a symbol that's like a backwards "c", two parallel lines, and a small "s". The center of the symbol is on the second line of the staff.
I think the symbol on the second staff is some sort of repeat sign, from the research I've been able to do, but I have no idea what the one on the third staff is for. I can provide more musical context if that's necessary.
The second staff is a violin part and the third staff is a viola part, if that's helpful too.