Colin Huggins was there with his baby grand, the one he wheels into Washington Square Park for his al fresco concerts. So were Tic and Tac, a street-performing duo, who held court in the fountain — dry for the winter. And Joe Mangrum was pouring his elaborate sand paintings on the ground near the Washington Arch.

In other words, it was a typical Sunday afternoon in the Greenwich Village park, where generations of visitors have mingled with musicians, artists, activists, poets and buskers.

Yet this fall, that urban harmony has grown dissonant as the city’s parks department has slapped summonses on the four men and other performers who put out hats or buckets, for vending in an unauthorized location — specifically, within 50 feet of a monument.

The department’s rule, one of many put in place a year ago, was intended to control commerce in the busiest parks. Under the city’s definition, vending covers not only those peddling photographs and ankle bracelets, but also performers who solicit donations.