You can usually see the stealth lights if you look into the grill.
Besides the old obvious as fuck Crown Victoria, be suspicious of 2013+ Ford Taurus and Explorer, 2006+ Dodge Charger and Dakota, 06-13 Chevy Impala, 11+ Chevy Caprice and both the Tahoe and Suburban.
Look for oversize mirrors, plugs on the roof and/or A pillar, lights inside the grill, extraneous lights inside the headlight assembly, lights tucked up behind the rear view mirror, steel wheels with or without wheel covers, and plugs or short antennas on the trunk lid.