.

[uplandrd2020]

..

[Dogkennelhillbilly]

1) you're being inconsiderate in some way. Raising wipers is a way of letting you know. Are you blocking a driveway or a dropped kerb? Are you parked in front of the house of one of those people who think they own the street in front of their house?

Or

2) there's no point to it

[TheArtfulDogger]

My money's on school children being mischievous

[Ginster]

If you put cctv in your car aren't you then giving them (or someone else) something to steal?

Only other thing to note - and unlikely really as it's outside your house but there has been press about people putting things on your wipers or wrapping things round them to make you delay getting into your car to rob you (extreme I know!) but sharing just in case!