If the sign was posted by the municipality it is an enforceable sign. The issue of it being private or public property is a red herring. It is within the highway right of way and deals with entering a public roadway and as such is enforceable.

The private property issue deals with issues solely on private property such as a mall parking lot, not where it adjoins a public roadway.

PA has obviously not adopted the uniform traffic code like many other states have which requires a full stop prior to entering any public roadway from any private property. As provided by others if there is no sign present one merely has to yield to traffic on the roadway.