Where I live we all have designated parking spaces, if your house has 2 bedrooms you have 1 space, 3 bedrooms or more you have 2 spaces.
My next door neighbours have 2 cars, and one space, not totally unusual for a modern household. However, they don't use their parking space, they park against the house opposite (which is shown in my drawing), it's side on to us as the street is an L shape and as it's a through road not a proper roadway it's not very wide, so cars parking opposite can make it difficult for all the households to park in our parking spaces and if they don't park tight to the wall its hard to get through sometimes.
I get people have visitors so people parking against the wall doesn't bother me, what bothers me is they don't bother paqrking in their space, they went away for 2 weeks a while ago in one car, and left the other parked against the house opposite.
Would it be unreasonable of me to knock on their door and ask them to use their space, or be passive aggressive and post a note through the door? Or as we're moving house later this year, just leave it?