Chicago's rats are a brazen, shameless group, as likely to stare back at you as they are to scurry away underneath that alley mattress. Every Chicagoan breathes a little easier when they see the Streets and Sanitation Department's yellow, ever-present "Target: Rats" signs advertising that their neighborhood vermin are about to get poisoned. Bill Healy was walking home from dinner Tuesday night near North Wolcott and West North avenues in Bucktown when he thought he saw one of those signs heralding the end for area rodents. But a closer inspection revealed that the sign actually read "Target: Bums."