In Feng Shui, umbrella means "scattered", so if you hang an umbrella in front of your neighbor's house, it means that the family is scattered and the wealth is scattered. So this kind of behavior is unlucky in geomantic omen.
If the neighbor's umbrella is hanging at the door, it is suggested to communicate with the neighbor and remind them to put it away. If they don't cooperate, they can choose to call the police.