If a person were looking for extra-Biblical evidence of the existence of the city of Bethlehem, one might direct one’s attention to a bulla, or a piece of clay used for sealing a document or object reported on back in 2012:
The bulla, measuring 1.5 cm, was discovered bearing the name of the city, written in ancient Hebrew script. The dig is underwritten by the Ir David Foundation.
A bulla would be impressed with the seal of the person who sent the document or object, and its integrity was evidence that no one had viewed or opened the document who unless authorized.
Three lines of ancient Hebrew script appear on the bulla, including the words: Bishv’at, Bet Lechem and [Lemel]ekh.
Eli Shukron, director of the excavation on behalf of the Israel Antiquities Authority, stated that the discovery appears to show that “in the seventh year of the reign of a king (it is unclear if the king referred to here is Hezekiah, Manasseh or Josiah), a shipment was dispatched from Bethlehem to the king in Jerusalem.”
Shukron dated the bulla to the seventh or eighth centuries BCE during a period in which bullae were used for taxation of shipments in the Kingdom of Judah.
He emphasized the bulla’s significance as, “this is the first time the name Bethlehem appears outside the Bible, in an inscription from the First Temple period, which proves that Bethlehem was indeed a city in the Kingdom of Judah, and possibly also in earlier periods.” source: https://www.jpost.com/Features/In-Thespotlight/Archaeologists-find-first-proof-of-ancient-Bethlehem
While Romans have been known to use boundary stones, this is clear evidence of communication being protected meant for a King following Royal Mail protocol which happens to also help solidify the claim of Bethlehem being an ancient city.