My parents had this happen once....but they have stained cedar siding so it makes a little more sense. I have no idea what they ever did about it though, but maybe can you tie something up there that would blow in the wind and maybe scare him away? Maybe just something like a dishtowel or hand towel? Although it should be light enough to flap in the breeze. Other than that I have no idea what you could do to get rid of him.

My dad also once had a cardinal that would constantly be pecking at the mirrors on his truck. It was mating season and the cardinal thought the bird in the mirror was a rival. Didn't hurt the mirror at all but my dad wasn't too thrilled about all the cardinal poop all over his truck.