This is an interesting one.

The symbol for ” Chemical weapon warning hazard“ appeared in an English field (see images here or hit crop circle connector link below) around the same time a British woman, Dawn Sturgess, reportedly died from exposure to a nerve agent called: Novichok.

Links:
https://www.aljazeera.com/news/2018/07/uk-dawn-sturgess-dies-exposure-nerve-agent-novichok-180708205638405.html
https://en.wikipedia.org/wiki/Hazard_symbol

Crop circle:

http://www.cropcircleconnector.com/2018/coneyburyhill/coneyburyhill2018a.html