Block diagram of state variable filter?
Vin could be a positive voltage or a negative voltage. The sign of the input signal is, largely, irrelevant; the negative sign simply inverts the input signal and has no impact on the form of the CLTF. The minus sign is just there to make the student think.

Also, the negative sign in the CLTF is wrong, the -K1/s block makes it negative f/b.