The Pennsylvania Dutch use these Hex signs to ward off evil and for good luck.
https://en.wikipedia.org/wiki/Hex_sign
Controversy over origins
There are two opposing schools of belief regarding the derivation of the name. The term hex with occult connotations may derive from the Pennsylvanian German word "hex" (German "Hexe", Dutch "Heks"), meaning "witch". However, the term "hex sign" was not used until the 20th century, after 1924 when Wallace Nutting's book Pennsylvania Beautiful was published.[8] Nutting, who was not a Pennsylvania native, interviewed farmers about their distinctive barn decoration. Before this time there was no standardized term and many Pennsylvania German farmers simply called the signs "blume" or "sterne" (meaning flowers or stars). However one farmer used the term "Hexefoos" in his description.[9] The term became popular with Pennsylvania Germans themselves during the blossoming tourist trade of southeastern Pennsylvania.
These signs were traditionally ordained with six-pointed stars.There is also the belief that the origin leading to the word "hex sign" is that English settlers mispronounced the German word for six, "sechs", as "hex".
In recent years, hex signs have come to be used by non–Pennsylvania Dutch persons as talismans for folk magic rather than as items of decoration. Some believe that both the Pennsylvania German barn design and hex designs originate with the Alpine Germans. They note that hexes are of pre-Christian Germanic origin; for instance, a circled rosette is called the Sun of the Alps in Padania (the Po Valley).[10] Based on this history, neopagans or Germanic heathens have taken up the practice of creating hex signs, incorporating other pre-Christian signs and symbols into the hex work. Gandee, in his book Strange Experience, Autobiography of a Hexenmeister, described hex signs as "painted prayers".[11]
Some view the designs as decorative symbols of ethnic identification, possibly originating in reaction to 19th century attempts made by the government to suppress the Pennsylvania German language.[2] Anabaptist sects (like the Amish and Mennonites) in the region have a negative view of hex signs. It is not surprising that hex signs are rarely, and perhaps never, seen on an Amish or Mennonite household or farm.[1]