Can anyone assist with what might be causing this and if they are removable? They all seem to be in front of the nail heads.
They are in neat rows, look to be about 16" apart.
My guess is nail pops under the siding.
That is only a guess. Your photos look like my house, same siding and shutters. Except after 8 years, I don't have those spots.
its sort of the reverse of the black dirt marks I see on ceilings after many years...right where the beams are....I wonder if you tried to clean the siding what would happened?