Came across this item, mentioned on another forum: [ame=http://www.youtube.com/watch?v=SvPXmwBOlsk]YouTube - Man's best friend is best weapon in war on drugs.[/ame] Looks like they're mainly targeting "dirty backpackers" who buy their tickets on the day of departure, pay cash (or use a prepaid credit card), and travel in coach.
Also, per that other forum, they're targeting those who wear hoodies while the they step off the train for a cigarette while the train is stopped in Reno.