Meaning
What does Marked Safe mean?
Marked Safe is a feature on Facebook, available for people, who were near a catastrophe, a terrorist attack or some sort of other crisis.
The feature was adopted by internet users as an exploitable meme format.
Origin
What's the origin of Marked Safe?
The tool was added to Facebook in October, 2014, inspired by the 2011 earthquake that shook the Japanese archipelago.
It became widely known and used after the terror attacks in Paris, in November, 2015.
Spread & Usage
How did Marked Safe spread?
The feature was turned into a meme following its spread in 2015 and by 2018, it appeared frequently in posts on Reddit, Imgur, iFunny as well as Pinterest.
As of 2021, the meme still appears sometimes, although its echo on the web is suppressed by much more popular jokes and memes.

External resources
- Los Angeles Daily News – What does it mean when friends are ‘marked safe’ on Facebook?