In the story, a scientist discovers that cities have more or less a gestalt consciousness, and that they communicate with each other indirectly through people. He decodes this communication, and begins communicating with a city by having people wear colored t-shirts and go to particular places.
The city he communicates with experiences a sudden and rapid downturn...he "asks" the city why, and the city indicates that the other cities think that "he" is crazy. Why? Because he hears voices from nowhere! Your voice!
Cool story...may have been in Amazing Stories, or Asimov...possibly Omni.
I believe I read it in the mid to late eighties, and it was a short piece in an anthology. I remember the anthology being the smaller, paperback-size like Asimov was, I think. It was definitely a researcher who dispatched volunteers with t-shirts...contemporary, non-fantasy setting. I'm nearly 100% sure on the t-shirt aspect.
UPDATE: from user @andrew, a much better synopsis that fit with my fuzzy memory:
Five years ago on an SF mailing list someone was looking for a story with this description:
Guy in bar is very depressed. Bartender asks him what's bothering him. Guy replies, "New York is going to kill us." First bartender thinks he's talking about an upcoming sporting event. Nope. Then bartender thinks he means that there's going to be some sort of rioting. "Did I say a bunch of people from New York are going to come here and kill a bunch of people?"
The guy tells his story: He's a sociologist who, looking at large-scale data on patterns of movement through the city, realized there was a pattern, and, after intensive study, cracked the code: Patterns of people moving in public areas actually formed an "uber-language," the massmind of the city itself speaking. Having figured out the language, he then runs an experiment, paying crowds of homeless people to move from place to place in the city, and begins asking the massmind questions.
The conversations take weeks, even months, but he's learning about the literal mind of the city. It's fascinating work. It's ground-breaking. Then, one day, the city has turned surly, and it answers him with hostility. When he inquires, the city tells him that other cities have sentenced it to death. New York City will be its executioner. "But, I don't understand. Why would they do that?" "Because I'm insane," the city tells him. "What do you mean? How can you possibly be insane. You seem perfectly rational." "I'm insane. I hear voices. I hear you.