Fence Down Sensor Alarm
This Alarm has to do with the Part Pins or Fence not fully retracting or a miss aligned sensor on a part pin. Generally, these part pins have sensors on machines when you have the option for an MLS, Full line or Half Line machine. These sensors are active to make sure the pins retract all the way to avoid a machine crash.
The Arrows are pointing to the Black Fence attached on top of pins.
Circled is a part pin that is under the fence and on both ends of the table on most machines. The sensors are on the body of the pins air cylinder, and you can't see them on all machines from the outside.