The Boston Post Road, which followed an already established Native American trail, was established in 1673 as couriers bringing mail to different locales in the colonies traveled the trail, which was then very rough and interrupted in several locations. Couriers would mark miles by hacking cuts into trees at intervals. After nearly a century, the road was straightened and improved somewhat between New York and Boston, and from 1753-1769 heavy stone markers were set at one-mile intervals, with the surveying supervised by Benjamin Franklin. Postal rates were set by the distances between one spot and the other.
There are only two extant markers surviving today in NYC. One is the 11-mile marker, which can be found on the grounds of the Morris-Jumel Mansion in Sugar Hill. Another is the 12-mile marker, embedded in the outside wall of Isham Park at Broadway and Isham Street. There are other surviving markers in towns like Mamaroneck and Hastings-on-Hudson.
On Delancey Street between the Bowery and Christie Street, you will find a tavern called the One Mile House (it has replaced its sign since this 2014 Street View photo). The Bowery is an existing section of the Post Road, and the first mile marker was placed along the old road at about Delancey as it was one mile north of City Hall in the 1760s, located at Wall and Broad Streets. After the “new” City Hall was built in 1812, all of the milestones along the lengthy route had to be moved. Thus, the 1-mile marker was moved to about Rivington Street and the Bowery. That marker survived until 1926, when a truck ran into it; however, there was a One Mile Tavern at Bowery and Rivington that lasted until the 1970s. This new One Mile House also recalls that milestone; it opened in the early 2010s.
Info from: The Bowery: The Strange History of New York’s Oldest Street by Stephen Paul DeVillo