Alien slave hunting

Had a strange dream last night.  Aliens from a planet around Deneb were looking for slaves.  They had three requirements for potential slaves: 

1.  They need something in common that is easily identifiable to aliens,
2.  There's got to be enough of them to make a good work force.
3.  They shouldn't be missed by their neighbors.

They took everyone with Confederate flags on their cars, trucks, and clothing.