My 1982-83 Antenna Specialists catalog calls this a 'slot' antenna.
It was available in 2 UHF ranges.....Model ASP-1000 for 450-512 MHz, and ASPA-1000 for 406-420 MHz.
I don't know of too many cars in today's era that this could be installed in other than something that already looks like a police car........Kinda defeats the purpose of undercover.