These miniature semaphores were placed adjacent to certain switches in block-signaled territory and were used to show switchmen that the adjacent block was occupied so they wouldn't throw the switch and cause an unexpected red  signal in the face of an approaching train. If I recall what happened was that when the block was occupied the little red semaphore arm would move up to the 45-degree position.

This particular set of indicators was located south of Fon du Lac on the line to Milwaukee at a place called Quarry, which was/is the location of a large marble quarry which ships stone out by rail. This location is still served today by Wisconsin Central although the line itself has been downgraded to 10 MPH and the signal system is long gone.

The third pic shows a somewhat unusual view of a semaphore signal taken from an adjacent overhead road bridge near the small town of Marblehead, WI located just north of Quarry and south of Fon du Lac.