They are like an arrowhead into the runway, depicted on CAA 250k charts.Shown at aerodromes having one or more IAPs outside controlled airspace. Such as Norwich (for a little while yet) , Manston, Lydd etc.
Whilst plodding aong at circa 75mph below 2000ft, I've always contacted the airfield concerned when passing in the vicinity,as I wouldn't want to spoil somebodies IAP training session for the sake of good communications and considerate airmanship.
But if it isn't practical to have that feature, I will lve with it 