The medal recognizes those military service members who were assigned to the U.S.-Mexico border at the period of time when the United States was on the verge of all-out war with Mexico. While US Army forces had moved past the border and into Mexico, the mission of the national guard units was to protect towns and ranches on the US side of the border from any attacks.
Many states that participated issued this type of medal to members of their national guard who participated in the Mexican Border Service in 1916/1917. Later, many of these units were re-organized and deployed overseas for the war in Europe
This medal retains its original ribbon and sewn-in pinback, it is also serialized along the rim and I would assume researchable via the PA national guard. Execellent example.