I live on Capitol Hill and regularly see parking enforcement checking cars, but if there are cars that you think are hanging around too long near you, you can report them at https://www.seattle.gov/police/need-help/abandoned-vehicles
This isn't Soviet Russia, it's not like I'll get an extra ration and a pat on the back for turning my neighbour in.
[1] This has gotten better since they've added a parking permit requirement.