If the neighbour knows about the escort, why aren't they confronting her about it? And why the bizarre non-threat of "the police drove by and have your reg. number"? Like you said, even if the police had by chance drove past, how does the neighbour know they took your reg? And if they did, why? Fucking idiots.
I'd just keep parking in the same spot. Leave a note for them on your windscreen saying you're just visiting a friend and what was with the bizarre note last time?