Historic England would like to remind the people of the UK that Halloween isn't only about eating low-grade confectionary until you start sweating, can't concentrate on anything and really need a poo, and is asking people to look out for real-world signs of the witchcraft world of the olden days.
The society would like the general population to stop taking photographs of their stupid little dogs and instead submit images of Apotropaic or Witches' marks spotted in and around old buildings, as these carvings indicate spots where symbols were placed hundreds of years ago in order to protect the occupants from attack by the weird. The CCTV camera alert stickers of their day, if you will.
Here's the sort of thing you should be looking out for:
Apparently they used to be really commonplace, hence there's no real record of them. But that could change if people can be convinced to look up from their phones for a bit and do a bit of gonzo historical reportage when near a thing that looks old.
Historic England's Duncan Wilson said: "Witches' marks are a physical reminder of how our ancestors saw the world. They really fire the imagination and can teach us about previously-held beliefs and common rituals. Ritual marks were cut, scratched or carved into our ancestors’ homes and churches in the hope of making the world a safer, less hostile place." [Historic England]