In 2008 Lost City had a blog post about a property marker seen at 909 Third Avenue in the mid-50s. He noted this Letter to the Editor from the NY Times:
Bronze Boundary Markers Provide Legal Protection
October 25, 1998
To the Editor:
The F.Y.I. column puts an inappropriate anti-corporate spin on the ''explanation'' for the little bronze pavement markers that announce: ''Property line. Permission to cross revocable at will.'' (''The Private Sector,'' Sept. 27)
The real reason for those markers, which you characterize as ''snide,'' has nothing to do with the preservation of ''corporate calm'' or the exclusion of vagrants and criminals, as you assert. Putting the world on notice that crossing is by revocable permission is a simple necessity to insure that the ancient doctrine of adverse possession doesn't rob the landowner of his land.
Under a legal principle we inherited from pre-Revolutionary English law, open use of land without permission and against the interests of the landowner can gain the user actual ownership of the land after 10 years. By placing the little bronze markers where pedestrians walk, the owners of the private property adjoining the sidewalks confirm that they don't intend to cede that land to the public.
AMNY Urbanite also had a 2008 post about a marker seen out front of the Haier Building on 36th between Broadway and Sixth (formerly a grand home to the now-defunct Greenwich Savings Bank):
Adverse Possession: Mind Your Property
... read more for an explanation behind these plaques, which are designed to prevent "adverse possession" of a property by someone who does not own it.