http://fusion.net/story/344884/sex-slave-bars-in-united-states/

Here is an article:

Sex-trafficking operates in a closed network, but oftentimes in plain sight. To the unacquainted, it’s easy to see without recognizing. Men who hand out “tarjetas de viejas” —or “chick cards”— on the street corners in New York, cantinas that charge excessively high prices for drinks, and D.C. cabbies who ask single men if they’re looking for action can oftentimes be signs of a trafficking network lurking just below the surface, experts say.

Maybe a DC cabbie has some of these cards?