In message , Christian
McArdle writes
However, recently a small number of strangers have started parking
here regularly and some leave their car here all day while they
are at work.

Let down all the tyres. Every time. It'll take them longer to move that day,
but they should get the message in future.

You really shouldn't do that

Nor should you put the sticker on the windscreen with silicone adhesive
as it will leave a smear which is next to impossible to remove over the
life of the windscreen. Whatever you do, don't stick polyurethane foam
up the exhaust, it's a very very bad thing to do.

--
geoff