Over the past 15 years, Dan Smith’s name and face have appeared on fliers in coffee shops, laundromats, and small businesses across New York City. The six-word slogan on each flier says: Dan Smith Will Teach You Guitar. The result is that Mr. Smith stays as busy as he wants to be, teaching his students how to play the guitar. Many enthusiastic students hang his fliers in new places. It’s their way of saying, “Dan Smith taught me guitar. He can teach you too.”