In the apartment complex of someone I know, there is a voodoo witch who sprinkles oil on the doors, gates, and walkways of the complex to ward off evil spirits.
In order to not benefit from this idolatrous service (or give the appearance of doing so), must my friend affix a hamsa or similar Jewish-ish talisman to provide independent protection from the evil spirits?
Note: I have seen a gemara about evil spirits lurking in the bathroom yet we do not put mezuzas there. If the purpose of the mezuza was to banish these spirits, we would certainly put one on the bathroom because of the great danger. Yet we don't. ergo we do not hold that mezuzas ward off evil spirits.