Being in PA the black dots are deffenitly probably artillery fungus. Very common in the Northeast from mulch. Below is a link of some information from Penn State University on the subject. In addition, I make sure I carry a print out of the article on the second link with me, when I run into a customer that has this problem with their property. It's helpful to show them and explain to them that the problem isn't fly crap, but a fungus. It's usually not too far afterwards that they end up replacing the mulch with decorative stone. Not much you can do to remove it on vinyl siding. You can scrap it off with your finger nail, but it leaves a stain in the vinyl. I talked to some folks at Eaco chem, and they recomended SafeRetore to remove the stains, but that stuff isn't cheap, and well let's just say not too plant friendly. But if you want a good weed killer, it turns anything brown in 2 minutes

JZ

Artillery Fungus- Frequently Asked Questions (FAQ)
ARTILLERY FUNGUS THREATENS HOMEOWNERS, MULCH INDUSTRY