On a trail that crosses private property, the owner of the land may grant permission to allow passage. This easement may be revoked at will by the property owner. Sidewalks in Manhattan are, of course, public rights of way, so it is unexpected, to say the least, to find a plaque declaring a patch of heavily-traveled sidewalk on Seventh Avenue to be private property. Yet such a plaque can be found directly across the street from the entrance to Penn Station. Is this a prank? Who would go to the trouble to cement it into the sidewalk?
PERMISSION TO CROSS
REVOKED AT WILL"