Why are the windows in a Kingdom Hall covered?

Jehovah's Witnesses use Kingdom Hals for worship. A church refers to the people who attend; it is not a building. Therefore, they do not cover their members.

During and after WW2, there was a lot of vandalism and backlash against Jehovahs Witnesses due to their neutrality regarding war. This resulted in damage to buildings and security issues for people attending. Today, safety glass is used on most Kingdom Halls. Window coverings are not required in such cases unless perhaps the heat of the sun creates uncomfortable conditions, which are not condusive to study, which is the purpose for the building. In such a situation, a moveable covering would be a simple, effective solution.