Earlier quoted context omitted.
The problem is the cops tend not to give a shit.
I understand that. But you cannot assume they won't help. These guys didn't even try contacting the police before hatching a late-night scheme. For what it's worth, in my (regrettably several) experiences with stalkers/harassers, this situation would have been taken extremely seriously. "Masked guy repeatedly visits at night to write threatening messages on car of single woman living alone" is... about as explicit as…
>Now it was time to call 999. My sister had already had a couple of police visits about the previous incidents, so they knew there was a problem linked to her flat and came round pretty quickly.