There is no 1000' school zone in Washington law.
You are exempt from the (unsonstitutional) Federal Law if you have a WA CPL in Washington.
You may only have a Pistol on school grounds when picking up or dropping off a student and you may not enter a building even if you are picking up or dropping off a student.
Regardless, if you were on private property right next to the school the Federal law would not apply.
#7 (signs) is a feel good measure as signs have no authority in Washington.