We applied Avigo Chilli Gel to the hand rails. The active ingredient, Capsaicin is transferred to the feet of the pigeons once they land on the gel. When the birds fly off and tuck their feet up next to their under parts, the chilli extract does its work causing a mild irritation.
Not sure a “mild irritation” accurately describes it (come on, you know how it stings when you've wiped your eye after cutting chillies - ouch!) but that’s what is says on the product label so we will go with it. Needless to say, the pigeons have avoided the area altogether since.
With the balcony being temporarily out of bounds for the residents, the gel was only an interim deterrent, but when we returned four weeks later to remove all trace of the gel we were delighted to hear that the gel had worked. Pigeons had landed they soon flew off again!
Obviously, with the gel being in a high traffic public area it wasn't possible to leave it for too long, however, when the gel is applied in areas not accessible by people, it acts as a long-term deterrent, only requiring two maintenance inspections a year to replace any gel that may have been worn away by landing birds. Worth considering if your office or building has some unwanted squatters.