In alt.home.repair, on Thu, 17 Sep 2015 12:59:08 -0700 (PDT),
wrote:

On Wednesday, August 9, 2000 at 3:00:00 AM UTC-4, olryfarr wrote:
Principally on the North side of my house, sided with white, textured vinyl,
during the summer months, I find small brown spots appearing that wipe off
easily with a cleaner and sponge. However they keep reappearing. On the
vinyl clapboards close to the deck, I notice bunches of the small brown
spots lying on the deck. My guess is small bugs, but I don't know. Has
anyone ever experienced this problem? Any ideas. Thanks. -Paul

I have small brown spots on vinyl siding. The seem to be in a certain pattern which in 1 on every siding. They are not raised and not bird poop. Tried pressure washing an no luck. What could they be?

Dirt attracted to the spot electrostatically because of a nail
underneath the siding?

I don't know if this can happen outside, but I saw it once inside in a
house where the oil furnace wasn't working right. Everywhere the
sheetrock was attached by a nail (or screw?) was a grey spot. Even
though there was wachamacallit, plaster, over the nail head. IIRC
where the sheetrock encased an I-beam, it was all grey.