CHICAGO — Each day at lunch Amy Le faces the same dilemma as she looks for a spot to park her bright green food truck in downtown Chicago. She needs a space close enough to hungry office workers but far enough away from the restaurants she knows will call police if she gets too close to their doors.

She finds a loading zone and sends out a tweet to her regular Duck N Roll customers so they can find the truck and buy her pre-cooked Vietnamese-inspired duck sandwiches before a police officer — who she worries might also be reading her tweets — notices she's parked illegally.

It's a calculated risk that Le is willing to take to sell her sandwiches. "I'm constantly looking over my shoulder for a police officer," she said.