Does that include the people play a music instrument off the platform? The people who perform and then "pass the hat" on the train?
I can 't find it mentioned on the MTA's website.
Artistic performances, included the solicitation of donations, are permitted provided they are done in accordance with the rules governing the conduct and safety of the public in the use of the facilities of the New York City Transit Authority and Manhattan and Bronx Surface Transit Operating Authority.
Look at "Permitted nontransit uses" in section 1050.6
In London, they have to have a licence, granted by the Underground authorities after an audition, and only when 'slots' become available. In New York I think anyone is allowed to busk.
You are required to have a permit for some public performances.
You must have a permit to use a sound device such as a loudspeaker, megaphone, or stereo in a street performance. Sound Device Permits are available at local police precincts during business hours. The fee is $45. You do not need a permit for street performances without a sound device.
You must have a permit to perform in or next to a park. A permit is also required to host a special event, distribute fliers, or perform at the Staten Island Ferry terminals. Performance activities are not allowed on ferry boats.
The Music Under New York (MUSIC) program coordinates special events throughout the transit system. MUSIC selects performers by audition. You do not have to be part of the program to perform in the subway system, but you must follow the MTA's rules of conduct.