Some examples

http://www.screens.ru/en/2010/9.html

https://www.digitalsignagetoday.com/articles/hacked-digital-...

https://securitytutorials.co.uk/hacking-digital-billboards/

https://www.screenly.io/blog/2018/11/16/digital-signage-hack...

https://www.mirror.co.uk/news/uk-news/giant-advertising-scre...