This is done to make it easier for emergency personnel or city workers to find a property. A rear house number could save a life. In delivering emergency help police, ambulance, fire seconds count. In the dark of night, a police officer in the alley cannot always be sure he is at the right house.
Accurate addresses facing the alley can save precious seconds.
A city ordinance requires that house numbers be a minimum of 3 inches high. They should be posted facing the alley on a garage or rear of the dwelling. The numbers are available at hardware stores. Rear numbers are not required for houses that do NOT abut on an alley. All city houses and buildings must be identified by a number.