Except I’m sure there are laws about starting fires on the streets of NY
if not, pass a law that to get the required permit to burn the flag you must pay a fee to have a firetruck standing by, you know for public safety, just in case ...
Also, raise the permit fee to cover the overtime for the 6 fireman crew plus 1 or 2 supervisors as well as a prorated share of their benefit costs, not to mention the appropriate cost to compensate for the wear and tear on the fire truck, etc.
Anyone lacking the required paperwork - lock em up, fine them the cost of a permit, expenses for the police that arrested them and bill them for their city provided accommodations.
If mayor big bird won't go along then approach it as a federal issue, presidential secret service teams require the permit for security/safety reasons and lack of cooperation will lead to withholding federal funds, a la the sanctuary city approach.