Belfast·SPG008 Advertising and Signage·Page 15·4.6.2(i)
Interference with navigational lights or beacons
Signs that could cause interference with navigational lights or aerial beacons are subject to refusal.
Those which cause possible interference with a navigational light or an aerial beacon.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/belfast/SPG008 Advertising and Signage.pdf