Speaking of coded visual communication in public places, archeologists have discovered medieval-era graffiti in churches that includes
pentagrams and other “witch marks” meant to ward off evil.
These were “…as central to the everyday lives of the medieval commoner as the next meal, the next harvest and the next year.” - Matt Champion, historian, archeologist, author
Images courtesy of the Norfolk Medieval Graffiti Survey
Portal 13 (2018). Shelter us from evil.