Pigeons can be a real pest especially is you live in a flat or apartment. the pigeons love to land on railings and their mess can be harmful if it becomes dry and is inadvertently inhaled.
So a simple little idea is to rub some petroleum jelly on the places that the pigeons land. They hate the feel of it. They might even slip off, which might be quite funny to watch.. It will make them find somewhere less slippery to land.
Another more direct approach was suggested in a tip sent into the site. To keep pigeons off your window sills use double sided tape with thumb tacks poking up through the top (the sharper the better) Nails work well also. Those pesky little birds can't stand or sit on your sills anymore!