That “upturned glass and paper in the sink” post is one of those viral clickbait-style headlines.
It usually refers to a simple home safety or pest prevention trick, but the exact meaning changes depending on the version:

• For pest monitoring: Some people leave an upturned glass over a piece of paper or sticky note to see if insects or rodents leave droppings or marks while they’re away. If there’s any sign when they return, they know pests were active.
• For leak/flood detection: Others put a glass upside down on a dry paper towel in the sink. If the towel is wet when they return, they know there was a leak or moisture problem.
• For electricity/water shutoff checks: In some versions, it’s more about ensuring nothing drips or leaks while you’re gone.

It’s not a widely recognized “official” safety method, but more of a home hack that people share online.