Liv Buli Michael Moore addresses the crowd at St. Mark’s Bookshop.

A book signing at St. Mark’s Bookshop by Michael Moore turned into a rally for the embattled store on Thursday, as the champion of the left exhorted patrons to continue buying literature in person.

“At some point you just have to stop and stand up and say: ‘No more,’ ” Mr. Moore shouted to the roughly 100 people packing the store on Third Avenue.

Mr. Moore’s appearance reaffirmed the sudden swell of affection for the Bookshop, which has gone from a store struggling to turn a profit into a symbol of the rapidly changing neighborhood in only one month.

“It comes down to a simple bookstore here on the corner of Third Avenue and Ninth Street in the East Village in New York City,” Mr. Moore said in between criticism of corporate executives and appeals to the store’s landlord, Cooper Union.

After addressing the crowd that formed a line out the front door, Mr. Moore signed copies of his new book, “Here Comes Trouble.” Bookshop co-owner Terence McCoy confirmed that all the publicity surrounding his struggling business was actually good for business. “We have never done a really big reading like this before, the phone has been ringing off the hook,” Mr. McCoy said. “It’s like having Elvis come to your bookstore.”

Liv Buli A younger fan of Michael Moore.

Mr. Moore said that he had gotten wind of the bookstore’s woes from friends who live in the neighborhood. “It’s the independent stores that really took my first book and made it a bestseller,” he said. “There is something about the humanness of this.”

He added that his favorite bookstore in his hometown of Flint, Michigan, Young & Welshans Books, had already met an untimely demise. “I have bought things on Amazon, but you never want to lose this,” he said. “It shouldn’t be an either-or thing. This is stimulating, to come into a store like this.”

The owners of the bookshop are expecting a response from Cooper Union regarding a reduction of their $20,000-per-month rent at the end of October. An online petition started in support of the longstanding business has more than 40,000 signatures.