Most likely, someone close to your apartment is feeding the little turds. At an old job, the neighboring workers behind our parking lot used to think it was cute to feed the birds at lunch. So we'd go home for the day and find our car hoods speckled with pigeon shit. We whined about it, they stopped feeding the birds, and it was solved.
I've heard that tying human hair to a balcony can keep them away. This page has some ideas:
http://www.getridofthings.com/get-rid-of-pigeons.htmI see bird strips around buildings in downtown areas. Those seem to work.
But if the apartment next to, or above you, is feeding them, you'll still get pigeon shit as they fly by.