The Police Cruiser from base GTA V.

Use https://gtaforums.com/topic/955449-iv-zolikapatch/ to unlock the 4 livery limit and make use of the +siren .ide flag

Vehicles.ide:
police2V, police2V, car, BUFFALO3, BUFFALO, VEH@STD, NULL, 50, 999, 0.2974, 0.2974, 0, 5, 1.0 ,0 ext_requi+ext_strong+livery+siren

handling.dat:
BUFFALO3 1700.0 7.5 85 0.0 0.0 -0.24 0.0 5 0.23 1.0 155.0 0.25 0.65 0.7 35.0 1.35 1.10 13.5 0.15 0.48 2.0 1.2 1.2 0.13 -0.13 0.0 0.5 1.0 1.0 0.8 1.5 0.0 25000 440010 1 0

txdp:
vehshareV, vehshare
vehshareV_hi, vehshareV

extra txdp for HQ interior:
police2V, vehshareV_hi
extra txdp for LQ interior:
police2V, vehshareV

carcols.dat (car3):
police2V, 133,133,133,