The second gen police Stanier 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:
policeV, policeV, car, POLICE, POLICE, VEH@STD, NULL, 100, 999, 0.2345, 0.2345, 0.2,2, 1.0 ,1, ext_requi+ext_strong+livery+siren

txdp:
vehshareV, vehshare
vehshareV_hi, vehshareV

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

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