See them coming, they scout first:

Fake UBER stickers
Fake magnetic company signs
Large vans
Suspect postal trucks
Suspect amazon delivery vans
Rental cars - usually Enterprise
Cops working with ICE

Out of state license plates
No plate at all
Your state plate w/some of the below
No front plate
Rear of vehicle-'patriotic' insignia
Lux cars, SUVs, big pick ups
Plate frame w/out of state insignia
Expired tags; gov't tags
Temporary plate
Erratic driving