Can anyone assist me with what might be causing these white spots all over my vinyl siding?
An alien invasion or a question for another forum would be my guess.
I know nothing about vinyl siding, not even how it is attached, but the placement makes me think of underlying nails or screws. Or the holes they make allowing air/moisture to move through the walls. Definitely a question for one of the house forums, not landscaping!
Click on "Other forums" from the one I linked below, and you will see a list of other house forums to choose from.
Here is a link that might be useful: Home Repair forum
I don't know anything about vinyl siding either. Barring karinl's idea:
Is there something above those areas with that same spacing that might be dripping on the vinyl? Unless you have an overhanging second story, I'd think probably something related to the eaves. What you're looking for is likely either white or metal (galvanized nails?), or else it would simply be locations/structures that make stronger drips: the force of the water would either be cleaning or abrading the vinyl.