A storeowner places a “No Smoking” sign in front of their store. This would be classified as a type of what factor.

The "No Smoking" sign would be classified as a health protective factor.

This is because it mainly aims at preventing possible diseases that can occur to those who are smoking as well as those who are inhaling the gases produced in the air from smokers.
This sign encourages active smokers to put off their cigarettes and throw them away and it protects the non-smokers from being subjected to the smoke produced from smokers. By this, it reduces the risk of cancer.