Ubiquiti Networks airGriM - Manual (Page 9)

9. The Release Button indicates the Antenna Feed polarization.
Confirm that the polarization indicator, V or H, on the
Antenna Feed matches the indicator on the Grid Reflector.
WARNING: The polarization indicators must match.
Vertical Polarization Horizontal Polarization
10. Re-attach the cable feed door to the Rear Housing. Ensure
the locking tab securely latches to the Rear Housing.