Related question: How is an area deemed unsafe and needing to be cordoned off?
An individual property owner can set up No Trespassing signs at the required intervals, and then law enforcement can prosecute people for ignoring those signs. But what about a municipality? In this case, it's a city in the state of New York. Can the mayor decide that a particular area is unsafe, and order that No Trespassing signs be put up? Can the legislative body (in this case, a Common Council) issue such an order?
I realize that the Common Council can alter the City Code but that takes time -- there needs to be a public hearing, etc. I'm talking about a short-term solution.
I spoke with the head of the local station of the state police, and he said that if the City put up such signs, and notified the state police with a jurat (i.e. in writing, with the required legal language), then they would do the enforcement.